Treatment of human polymorphonuclear leukocytes (PMN) with anthralin (0.2-50 micrograms/ml) results in dose-dependent inhibition of nondirected as well as directed migration (chemotaxis) against the synthetic tripeptide N-formyl-methionyl-leucyl-phenylalanine (FMLP), the complement fragment C5a and leukotriene B4. Polymorphonuclear leukocytes (PMN) pretreated with anthralin at concentrations which inhibit cell motility also show a dose-dependent inhibition of superoxide anion generation. In contrast to anthralin two derivatives (danthrone and anthralin dimer) were ineffective. Specific binding of [3H]FMLP to neutrophil membrane receptors was impaired by anthralin at concentrations 5-10 fold higher than those which were inhibitory for cell function. Release of beta-glucuronidase from azurophilic (lysosomal) granules provoked by various chemotaxins in the presence of cytochalasin B was not affected by anthralin over a wide range of concentrations. Also there were no signs of cytotoxicity e.g., leakage of cytoplasmatic lactate dehydrogenase (LDH) caused by anthralin, These data indicate that neutrophil functions may become substantially altered by anthralin. The effective dosages correspond to concentrations obtained in vivo after local application. Danthrone as well as anthralin dimer, known to be clinically ineffective, showed no effects upon PMN function. It is suggested that anthralin via a free radical mechanism alters sensitive sites at or in the cellular membrane including receptors.