Thirteen Campylobacter-like organisms (CLOs) isolated from rectal cultures from homosexual men were studied. Like catalase-positive Campylobacter species, CLOs were curved gram-negative rods that did not grow aerobically, were motile, were oxidase- and catalase-positive, and did not utilize glucose. However, CLOs could not be classified within any of the Campylobacter species because they grew slowly and had unusual colony morphology; did not grow at 25 C, hydrolyze hippurate, produce H2S in triple sugar-iron agar, or tolerate 2% NaCl; were inhibited by 30-micrograms disks of nalidixic acid; and tolerated 1% glycine and 0.04% triphenyltetrazolium chloride. Three groups of CLOs were identified based on differences in nitrate reduction, growth at 42 C, and sensitivity to cephalothin. By the colony hybridization technique, whole-cell DNA isolated from a strain in each CLO group hybridized with DNA from other strains in the same group, but not with strains in other groups or with reference strains of catalase-positive Campylobacter species.