A new selective medium, GC-Lect, was compared with modified Thayer-Martin medium (MTM) for isolation of Neisseria gonorrhoeae. Cultures from 620 sexually transmitted disease clinic patients were directly inoculated onto both media, placed in candle extinction jars, and incubated. N. gonorrhoeae was isolated from 175 (29%) of 607 genital cultures, 3 (3%) of 88 pharyngeal cultures, and 6 (29%) of 21 rectal cultures. Ten cultures were positive only on GC-Lect, and 3 were positive only on MTM. In 3 of the 10 cultures positive only on GC-Lect, overgrowth of a Capnocytophaga sp. may have obscured growth on MTM. In this study, vancomycin-susceptible (MIC, <4.0 ,ug/ml) N. gonorrhoeae was isolated on both media, and none of the isolates missed by either medium were susceptible to vancomycin. No differences were noted between the two media in time required for isolation of N. gonorrhoeae. While isolation rates of N. gonorrhoeae were similar, suppression of nongonococcal bacterial species by GC-Lect was superior to that by MTM. GC-Lect is equal to MTM for detection of N. gonorrhoeae and is superior for suppression of normal flora.