SUMMARY BACKGROUND: Dual HIV-1/HIV-2 seropositivity (dual seropositivity) is common in West African countries including Ghana. The diagnosis of dual HIV-1/HIV-2 infections is however complicated as HIV-2 DNA is more often not detected in dual seropositive individuals. OBJECTIVES: To detect the presence of HIV-1 and HIV-2 pro-viral DNA in dual seropositives and to determine the correlation between HIV-2 antibody titers and presence of HIV-2 DNA. The growth kinetics of HIV-1 and HIV-2 in vitro were also determined using plasma and lymphocyte cultures. DESIGN: Cross-sectional study SETTING: Urban and semi-rural HIV/AIDS clinics PARTICIPANTS: 13 dual HIV-1/HIV-2 seropositives from Agomanya and Accra RESULTS: HIV-1 DNA was detected in uncultured peripheral blood mononuclear cells of all 13 patients but HIV-2 DNA in 4 (30.8%). HIV-2 antibody titres were not useful in determining the presence or absence of HIV-2 DNA (P=0.28, Mann-Whitney U test). HIV-2 specific antibody was detected in 12 of the 13 dual seropositives by peptide-inhibition, the only patient with an Innolia gp36 band rating of 1+ was shown not to be reactive. HIV-2 grew efficiently in the presence or HIV-1 in vitro. CONCLUSION: HIV-2 DNA may not be detected in all dual seropositives thus not all of such patients may need drugs effective against HIV-2. Peptide based assays will be useful for correctly diagnosing dual seropositivity. Since HIV-2 may grow efficiently in the presence of HIV-1 and no commercial HIV-2 HIV RNA tests are available, dual seropositives on HAART need to be monitored to determine if a lack of immune restoration may correspond to an efficient suppression of HIV-1 RNA levels.