Humoral and cell-mediated immune responses were assayed following a 6-day exposure of LAF1/J mice to a 1.50 Tesla (1 T = 10(4) Gauss) stationary magnetic field. In tests of the immune response to sheep erythrocytes, the number of Jerne plaques formed by spleen lymphocytes and the level of serum IgM were not significantly different for the exposed mice in comparison with control animals. Tests for mitogen-induced lymphocyte proliferation also demonstrated no significant differences in the response of spleen lymphocytes from exposed and control groups of mice.