The objective of the study was to determine whether HIV infection favors the acquisition of Coxiella burnetii infection or increases the frequency of symptomatic Coxiella infections. A total of 754 subjects were tested for Coxiella antibodies: 596 intravenous drug users (IVDUs) (306 HIV-infected IVDUs matched by aged and sex with 291 non-HIV-infected IVDUs), and 157 healthy puerperal women matched to the IVDU women. A total of 520 patients with Q fever were tested for HIV antibodies. The seroprevalence of Coxiella antibodies was similar in the 2 groups of IVDUs (19.3% of HIV + IVDUs vs 22.9% of HIV - IVDUs). Likewise, there was no difference in the prevalence of Coxiella antibodies in the groups of IVDU women and healthy women. Of the 520 subjects with acute Q fever, diagnosed between 1987 and 1992, only 4 (0.77%) had HIV infection. The proportions of HIV-infected subjects in the population of patients, with Q fever, of 20-39 years of age (the age of maximum incidence of both HIV and Coxiella infection in our region), coincided with the estimated proportions of HIV subjects in the respective general populations of the province. In conclusion, infection by Coxiella burnetii was not more frequent among HIV-infected subjects. It is not likely that Coxiella infection produces symptomatic infections more often in HIV-infected subjects.