The purposes of this study were to: 1) determine the time course of changes in serum enzyme activities and muscular soreness following muscular exercise, 2) quantify the relative amounts and importance of intensity and duration of muscular exercise in inducing elevated serum enzyme activities and muscular soreness in untrained individuals, and 3) determine the correlation between magnitude of soreness sensation and level of post-exercise serum enzyme activity. It was determined that the highest serum enzyme activities and muscular soreness sensation occurred 8-24 h and 48 h post-exercise, respectively. Intensity and duration of exercise were varied by adjusting the percent 10-repetition maximum (% 10RM) and number of contractions (NR) performed. Increasing intensity and duration of exercise resulted in corresponding increases in serum enzyme activities and muscular soreness. High-intensity, short-duration exercise (80% 10RM, 170 NR) resulted in greater serum enzyme activities and muscular soreness than long-duration, low-intensity exercise (30% 10RM, 545 NR). Most subjects experiencing high levels of muscular soreness were unable to lift resistances of 90% 1RM, 48 h post-exercise. These findings indicate that a positive relationship exists among exercise performed, serum enzyme activity 24 h post-exercise, and muscular soreness. Increased intensity and duration of exercise produced increased serum enzyme activities and muscular soreness, with intensity having the more pronounced effect.