The objective of the present studies was to determine whether hormones influence the level of IgA in tears of rats. Our results demonstrated that IgA concentrations in tears of male rats were significantly higher than those of females. This difference appeared to be due to an effect of androgens. Castration of male rats led to a significant decline in the content of tear IgA. Administration of testosterone offset this response and stimulated a time-dependent accumulation of IgA in tears of orchiectomized rats. This hormone action was only elicited by androgens, and not by other classes of steroid hormones. The testosterone-induced increase in tear IgA levels may have involved enhanced local production of IgA, and was found to occur in parallel with an elevation in tear secretory component concentrations. These findings indicate that androgens may regulate the ocular secretory immune system of the rat.