When 55-year-old Boniswa Pityana heard about the death in police custody of black leader Steve Biko last September, fear gripped her twice over.

Like Biko, two of her sons, Barney, 31, and Lizo, 20, were being held by the same incommunicado detention. Moreover, Biko had been Barney Pityana's best friend.

Pityana, the principal of a black nursing school in East London, went straight to the police station in Port Elizabeth and asked to see her sons, only to be told it was impossible but a visit would be arranged.

Before that could happen, however, Pityana received more bad news. In October, her third son, 17-year-old Sipo and Barney Pityana's wife, 30-year-old Dimza, were picked by police, leaving her with four imprisoned family members and the care of a 7-year-old grandchild.

The Pityanas were among the 240 people the government says it was holding as of last December under the dreaded Section 6 of South Africa's terrorism law which forbids any communication with family or lawyers.

The government said another 61 were being held under Section 10 as a preventive measure. These prisoners may receive family visits. Unofficial estimates name a figure of close to 800 for the number of all political detainees who were held for various periods during the whole of last year.

Like so many other black South African mothers whose children have been detained by police because of the unrest in black communities in 1976 and 1977, Pityana went through "agony and anxiety" about her children's welfare, sustained only by the cliche that 'no news is good news.'

Last week, Pityana finally saw her eldest son in person for the first time since he was arrested last August. "It was a terrific relief," she said.

None of the Pityanas have been charged with any crime. Lizo and Sipo have been released and Dimza, like her husband, can receive visitors regularly.

The mother of Steve Biko, who died of head injuries while in police custody, was not so lucky. "I miss Steve most in the evenings because we were always together for supper," said Alice Biko, 58, as she sat, still dressed in black, in the tiny living room of her five room house where she lived with her son.

"Steve's death made a great difference to me because I depended a lot on him," she said, smoothing the apron which covered her dress and fingering the bottle of pills she takes for her diabetes. Her husband died when Steve was three years old.

Biko was the 42nd person to die in police custody since detention whithout trial was introduced in South Africa in 1963. Because of this, Alice Biko said she always feared something similar would happen to her son though she never expected it would be so soon.

The friendship of Steve Biko and Barney Pityana goes back to their high school days when both were expelled on suspicion of encouraging a student strike. Together they formed the all-black South African Students Organization (saso) and both were prime movers in founding South Africa's black consciousness movement. For their opposition to government policies, they were both given five year banning orders in 1973 which restricted them to their respective homes and prohibited them from receiving more than one visitor at a time.

Boniswa Pityana's first brush with the security police came when they picked up her son to give him his banning order.

"I felt terrible becuase I had never had contact with the security police before. It was always at a distance because it was happening to other people. The impact on me was very great," she said.

Barney Pityana's banning, and his subsequent detention along with his wife and brothers for their political opposition to the white minority government has made the Pityana family members local heroes among the blacks in Port Elizabeth.

"It affects us financially because Barney is not earning. I have to look after the family," Pityana said."Families are disorganized and children are left orphans," by indefinite detentions, she added, telling how 7 year old Loyiso, daughter of Barney and Dimza cried bitterly when police arrested her mother.