Chemoattractive properties of Neisseria gonorrhoeae were studied by measuring leukocyte migration in agarose gel. Human serum albumin (0.5%) was present in the gel and normal human serum was excluded from all components of the assay. Viable cell populations and lysates of colonial types F62T1, F62T2 and F62T3 induced migration of polymorphonuclear leukocytes. Chemotactic activity of the lysate was not altered by heating at 100 degrees C for 10 min and was retained in the 12 100 g supernatant fraction of the heated lysate. Fractionation of the supernate by Sephadex G-100 chromatography showed that the chemotactic activity was associated primarily with an absorbance peak at 280 nm of relatively low mol. wt. The chemotactic activity of this fraction was lost after dialysis and the peak was no longer present in the Sephadex G-100 elution profile of the dialysed supernate. The gonococcal leukotaxins were sensitive to digestion by trypsin, pronase and amyloglucosidase, but insensitive to treatment with RNAase, DNAase or lipase at pH 5.7-7.1.