Interactions of Neisseria gonorrhoeae with nonleukocytic eucaryotic cells including tissue culture cells (either primary or continuous lines), human sperm, and buccal mucosal cells appear to be influenced primarily by the presence or absence of pili on the bacteria. In this context, piliation enhances attachment to or association of microorganisms with the eucaryotic cells. Pili, on the other hand, appear to reduce interaction of N. gonorrhoeae with mouse peritoneal macrophages. Other groups have demonstrated that pili reduce phagocytosis of gonococci by neutrophils, but in out studies this affect is secondary to that dependent on "leukocyte-association" factor. The presence of such a factor is correlated with a particular protein found by polyacrylamide electrophoresis. Adherence among N. gonorrhoeae varies and results in colony forms of different coloration or aggregation characteristics. These different coloration forms correlate with the protein patterns of gonococci as found in polyacrylamide electrophoresis and also with the susceptibility of gonococci to killing by trypsin.