Treatment of the pre-B lymphoid cell line 70Z/3 by interleukin-1 alpha (IL-1 alpha) and gamma-interferon (IFN-gamma) induces kappa-immunoglobulin light chain gene expression resulting in surface IgM expression. In this study we examined changes in total intracellular magnesium concentration [Mg]i, in 70Z/3 cells following lymphokine stimulation. After 30 min of treatment, [Mg]i increased by delta [Mg]i = 2.8 +/- 1.1 mM (n = 10, p < 0.025) with IL-1 alpha, and by delta [Mg]i = 3.0 +/- 1.6 mM (n = 8, p < 0.05) with IFN-gamma. After 4 h of treatment, the effect of IL-1 alpha was sustained, delta [Mg]i = 4.0 +/- 0.8 mM (n = 4, p < 0.01), whereas that of IFN-gamma diminished, delta [Mg]i = 0.2 +/- 0.6 mM (n = 7). These cytokines did not induce measurable changes in cell water volume indicating that the lymphokine-induced increase in [Mg]i represented Mg2+ influx.