In vivo suppression of neutrophil chemotaxis in humans by orally and topically administered tetracycline (TCN) was examined using both modified Boyden chamber and skin chamber assays. Chemoattractants were derived from serum complement and bacterial culture supernates. The results showed that oral TCN caused significant suppression of neutrophil chemotaxis when measured by both assays and both sources of chemoattractant. Furthermore, application of a commercially available topical preparation containing TCN caused local suppression of chemotaxis as measured by the skin chamber assay. These results show that TCN does suppress neutrophil migration in vivo, and they provide support for an anti-inflammatory effect of TCN mediated in part by suppression of neutrophil chemotaxis.