In recent years, there have been sporadic reports of aberrant manifestations of syphilis and a changed syphilis serology in AIDS patients, which might indicate difficulties in diagnosing the infection and monitoring the response to penicillin treatment. Six male patients aged 25 to 42 years with asymptomatic HIV infection and secondary syphilis were retrospectively compared with a control group of seven HIV-negative males aged 26 to 52 years with secondary syphilis. All patients presented with macular-papular exanthema of secondary syphilis; in all cases it was also their first episode of the disease. The median WR titre was 13 (range 11 to 20) in syphilis patients with HIV and nine (8 to 14) in the control group (p = 0.1). The median time until WR was found non-reactive after penicillin was four months (3 to 16) and five months (3 to 9), respectively (p = 0.8). Thus, in this small series there was no statistically significant difference in the WR-titres of asymptomatic HIV positive and HIV negative patients with secondary syphilis, although there was a tendency towards initially higher WR titre in the HIV group, as reported by others.