A balance study was conducted to determine the minimum requirement for manganese (Mn) and to examine the effects of Mn depletion. Seven male subjects, age 19-22, were fed a Mn-adequate diet of conventional foods (2.59 mg Mn/d, 135 mg cholesterol, and P:S ratio of 0.86) for 3 wk to establish base-line data. Then a purified diet containing 0.11 mg Mn/d was fed for 39 d (depletion), followed by two 5-d periods of 1.53 and 2.55 mg Mn/d (repletion). Diets, feces, urine, and integument were analyzed for Mn, and blood was analyzed for Mn, cholesterol, and other constituents. Plasma levels of cholesterol decreased from 170 to 152 mg/dL during the base-line period, and then to 142 mg/dL at the end of depletion, but did not respond to 10 days of repletion. A fleeting dermatitis, Miliaria crystallina, developed in five of the seven subjects at the end of depletion, but disappeared as repletion began. The minimum requirement for Mn on this purified diet, calculated by the factorial method using Mn balance at three levels of intake was 0.74 mg/d. This requirement would be increased to 2.11 mg/d if the obligatory loss was combined with the lowest individual percentage of retention.