We examined the effect of the nature of the stimulus on the chemical composition of human tears. The protein concentration of emotional tears from women exceeded that of irritant-induced tears by 24% (P less than .01). Polyacrylamide disk gel electrophoresis disclosed no significant difference between the distribution of positively or negatively charged proteins of irritant-induced and emotional tears. Manganese concentrations in tears (30 ng/ml) exceeded serum concentrations from the same subjects by 30-fold. These manganese concentrations in tears were considerably less than previously reported values. We found no differences for the concentrations of protein or manganese in human tears between the sexes.