We have purified pili from isogenic opacity colony variants that were derived from 14 gonococcal strains. Pili purified from opaque colonies of one strain usually differed from pili purified from transparent colonies of the same strain. In 10 of the 14 strains examined, the apparent subunit molecular weight of pilin isolated from the opaque variants was larger than that seen with pilin obtained from transparent variants. In addition there were demonstrable intra-strain differences in the isoelectric point and buoyant density of pili derived from the opacity variants. Because gonococci express differing opacity phenotypes during the menstrual cycle, it is possible that the pili of these organisms may also alter in vivo.