Proliferation of male versus female human erythroblasts on addition of androgen. Cell numbers from cultures of male versus female cord blood donors (pregrown for 8 days in the absence of sex steroids) were counted daily in an electronic cell counter, and cumulative cell numbers determined (Figure 2; see “Materials and methods”). For clarity, values are shown for every third day only; for the full data set, see supplemental Figure S2. Cells were cultivated either under standard proliferation conditions (control, ♦), or in the presence of 1 μM testosterone (▪) or testosterone plus the androgen antagonist cpa (1 μM; ○). Error bars are SD of mean; n = 3.