Two gunmen sought by Northern Virginia police in connection with a series of pharmacy holdups have struck again, according to Fairfax County police.

The men, dubbed "Butch" and "Sundance" by one of their victims, robbed the Centreville Pharmacy, 5808 Centrville Rd., late Thursday afternoon, police said. Two customers and a clerk were forced at gunpoint to lie on the floor while the pharmacy owner, Irving Beller, 46, gave the robbers drugs and cash.

"They asked for cocaine, for Valium, amphetamines, just about every controlled drug - and by name," said Beller, who said he put an unspecified quantity of Dilaudid in a plastic bag held by one of the men.

Then they must have gotten nervous, said Beller, "because they said, "just get the cash"," and took money from the cash register and left, the owner said. "They seemed to know what they were going," said Beller, who said the robbers made off with $500 to $600 in cash and drugs.

Police described the gunmen, one white and one black, as being in their 20's.

Thursday's robbery appears to be the 10th in a series that began May 5 with the holdup of Preston's Pharmacy on North Glebe Road, Arlington.

"We are regarding the cases as related," said Fairfax County police spokesman Warren Carmichael. "The description of the men, the meth d of operation and the pattern are similar."