Human peripheral blood B cells were separated from monocytes and T cells, depleted of null cells by an anti-Leu 9 rosetting technique, and fractionated on discontinuous Percoll gradients to yield a highly purified, small dense B-cell population. These cells responded F(ab′)2 goat anti-μ at 10 and 100 μ/ml with membrane depolarization (measured by immunofluorescence with 3,3′-dipentyloxacarbocyanine dye) at 1 h, cell volume enlargement by 48 h, and modest thymidine incorporation by 72 h. They also responded to the 12-kd human B-cell growth factor of Maizel with membrane depolarization, but not with cell volume increase. F(ab′)2 anti-μ and B-cell growth factor together induced greater depolarization than was seen with either alone, but there was no synergy. The cell volume increase seen with F(ab′)2 anti-μ was not increased by B-cell growth factor. Comparison of data analysis methods showed that mean fluorescence intensity most readily detected significant depolarization. We conclude that in human B cells: (1) depolarization may be a "general response" to a variety of membrane stimuli, because F(ab′)2 anti-μ and B-cell growth factor acting through different receptors both induce it, and (2) depolarization does not inevitably lead to cell volume increase.