1. In a widely used procedure for measuring estrogens in non-pregnancy urine(1), 0.01 to 0.05% of a 24hr specimen is taken for analysis. 2. There is an inverse relationship between 24hr urine volume (chi) and creatinine concentration (81 observations on 75 women; r = -0.780; creatinine (g/iota) = 2.34 -0987 chi(iota); P less than 0.001). 3. The data suggest that, when 24hr output is unknown, creatinine levels may be used to select the amount of urine for estrogen analysis. 4. Volumes found to contain 0.01 - 0.05% of a 24hr specimen were: -- (formula: see text).