A simple, rapid, reproducible method for quantification of lower extremity muscle strength was standardized. The time needed to stand 10 times from a standard chair was recorded in 139 healthy subjects, aged 20 to 85 years (77 men, 62 women). Reproducibility was 6.8 percent (+/- 3.4 percent). Neither height nor weight was related to time in either sex. Weight was related to time (p less than 0.05) after adjusting for age, but this effect was slight compared with the effect of age alone. A highly significant (p less than 0.0001) relationship between time and age was found in both sexes. Younger men performed better than younger women, although this difference was lost in the older age groups. The results of this simple test correlated well with published data on the strength of knee flexor and extensor muscles in groups of men and women of various ages. This method was used to evaluate serially six consecutive patients with classic polymyositis or dermatomyositis. Improvement after treatment with prednisone used alone or in combination with azathioprine or methotrexate was found in all cases.