NEW YORK, JULY 6 -- The Dow Jones industrial average today regained much of the ground it had lost on Thursday, adding 25 points in the slowest trading of the year.

The average of 30 industrials climbed 25.74 to 2904.95, finishing the week with a net gain of 24.26 points.

Advancing issues outnumbered declines by about 8 to 5 in nationwide trading of New York Stock Exchange-listed stocks. Volume on the floor of the Big Board came to 111.73 million shares.

Eli Lilly rose 1/4 to 86 1/2 and Genentech gained 1/2 to 29 1/2. A research study published this week reported evidence that a growth hormone produced by the companies can reverse some of the effects of aging in older men. Elsewhere in the pharmaceutical sector, Abbott Laboratories rose 3/8 to 41 5/8; Pfizer gained 1 to 65 7/8; Rorer Group was up 1 3/8 to 74; and Syntex rose 1 1/4 to 60 1/2.

A broad range of consumer products issues also showed strength, benefiting, like the drug stocks, from investors' search for recession-resistant growth companies.

General Mills advanced 1 7/8 to 90 1/2; CPC International 2 1/2 to 82 1/4; Kimberly-Clark 3 1/2 to 78 1/4; Pepsico 2 1/8 to 79 7/8; and Philip Morris 1 3/4 to 49 1/4.

The NYSE's composite index of all its listed common stocks gained 1.33 to 195.78. Standard & Poor's industrial index rose 3.43 to 422.32, and the S&P 500 index was up 2.74 at 358.42. The Nasdaq composite index for the over-the-counter market gained 1.34 to 460.53. At the American Stock Exchange, the Market Value Index closed at 358.87, up 0.38.