Thirty women, divided among three different age groups, i.e. 30 years (range 26-35; n = 10), 50 years (range 46-55; n = 10) and 70 years (range 66-75; n = 10) volunteered as subjects for examination of the characteristics of the muscle cross-sectional area (CSA), maximal voluntary isometric force, isometric force-time and relaxation-time of their leg extensor muscles. The CSA of the quadriceps femoris muscle in the youngest age group was slightly larger (NS) than in the middle-aged group and much larger (P less than 0.01) than in the oldest age group whose CSA was markedly smaller (P less than 0.01) than the middle-aged group. Maximal force in the youngest group was slightly greater (NS) than in the middle-aged group and much greater (P less than 0.01) than in the oldest group whose values were markedly smaller (P less than 0.05) than the middle-aged group. The individual values in CSA correlated with maximal force both in the total subject sample (r = 0.82; P less than 0.001) and in the three age groups separately (r = 0.72; P less than 0.01; r = 0.86; P less than 0.01 and r = 0.67; P less than 0.05, respectively). When the force values were related to the CSA of the muscle, the mean values of 45.4 N.cm-2, SD 5.6, 47.6 N.cm-2, SD 5.0 and 46.8 N.cm-2, SD 7.0 for the three groups did not differ significantly from each other.(ABSTRACT TRUNCATED AT 250 WORDS)