Much attention has focused on environmental estrogenic chemicals such as para-nonylphenol which disrupt various tissues via the estrogen receptor. Ne studied effects of para-nonylphenol on gelatinase secretion by human lymphocytes in vitro. para-Nonylphenol (0.05-50 muM) dose dependently suppressed 92 kDa gelatinase secretion. The suppressive effect of 25 and 50 muM para-nonylphenol was completely blocked by tamoxifen. Ne also studied the effects of paranonylphenol (0.05-50 muM) on 92 kDa gelatinase secretion by human leukemia U937 cells. para-Nonylphenol suppressed 92 kDa gelatinase secretion in a dose-dependent manner. The suppressive effect of 50 muM para-nonylphenol was completely blocked by tamoxifen. Estradiol did not significantly suppress 92 kDa gelatinase secretion. Our results suggest that paranonylphenol suppressed 92 kDa gelatinase secretion via the estrogen receptor, however, para-nonylphenol interacts with the estrogen receptor in a manner distinct from estradiol. As this assay system is simple and rapid, it may prove useful to evaluate toxic effects of para-nonylphenol on human blood cells.