Urines of 6 normal subjects, collected during three consecutive 12-hour periods, were examined for proteinuria and albuminuria. During the first period, subjects were kept in the upright position, and during the next two periods in the recumbent position. Both position (upright and recumbent) and the urine collection period (day or night) significantly modify protein and albumin excretion. Proteinuria is more sensitive to different posture and albuminuria to different times of urine collection.