The relationship between serum testosterone (ST), body composition, and static strength was studied in 26 college females and 16 male college football players. In addition, the transient effect of weight training on ST was studied in 10 college males (5 skilled and 5 unskilled weight trainers), 12 male high school students, and 5 female college students. ST, measured by radioimmunoassay, ranged from 333.7 to 848.1 ng/100 ml in males, and from 32.8 to 121.5 n/100 ml in females. The high school subjects had significantly lower levels of ST. Correlations between serum testosterone, body composition (measured by densitometry), and static strength (grip and backlift) were nonsignificant in males and females. Comparisons of subjects with the highest and lowest levels of testosterone within each sex showed no significant differences in strength or body composition. Serum testosterone increased 111.4 +/- 96.l ng/100 ml (X +/- SX) following a weight training session in the male college group, but failed to increase in the college females or high school males. There were no significant differences in testosterone increases between the skilled and unskilled male weight trainers. Maximal exertion may be necessary for an increase in serum testosterone to occur. Lack of an increase in testosterone by high school males or college females may have been due to a submaximal effort during the weight training exercise.