The percentage of gonococcal isolates in King County, Washington, requiring citrulline and uracil (CU auxotype) increased from 1.6% in 1986 to 16.5% in 1997. Among men, urethral infection with the CU auxotype (n=93), in comparison with infection by other auxotypes (n=1211), was associated with coexisting chlamydial infection, younger age, heterosexual contact, and fewer new recent partners (P<. 05). Among heterosexual men, urethral infection with the CU auxotype, compared with infection with other auxotypes, less often produced symptoms of urethral discharge (75% vs. 92%) or dysuria (47% vs. 74%) or signs of moderate or profuse urethral discharge (57% vs. 89%, P<.05 for each comparison), produced symptoms of longer duration (7. 0 vs. 4.5 days, P<.01), less often resulted in urethral smears showing gram-negative intracellular diplococci (67% vs. 95%, P<.01), and thus more often was erroneously diagnosed as nongonococcal urethritis. Several mechanisms could explain reduced inflammatory response to the CU auxotype and its recent spread.