INTRODUCTION Differentiating between HIV-1 and HIV-2 infection is the first step to understanding HIV transmission, epidemiology and pathogenesis in geographical areas where both viruses circulate. In Cuba, positive results in mixed HIV-1/2 screening assays are confirmed by HIV-1 Western blot. Indeterminate results constitute the main limitation of this test and HIV-2 infection is among their possible causes; hence the importance of second-stage screening and confirmatory tests for HIV-2 infection. OBJECTIVE Investigate the contribution of HIV-2 antibodies to negative or indeterminate HIV-1 Western blot results in serum samples from 2005 through 2008 in Cuba. METHODS HIV-2 reactivity was studied using the ELISA DAVIH-VIH-2 diagnostic kit (Cuba) in 1723 serum samples with negative or indeterminate results for HIV-1 Western blot from January 2005 through December 2008. Duplicate sera reactive by ELISA were confirmed by HIV-2 Western blot, results interpreted according to WHO criteria. The epidemiological interview established by Cuba's National Program for Prevention and Control Sexually-Transmitted Diseases and HIV/AIDS was applied to HIV-2 Western blot-positive patients. RESULTS Among all sera studied, HIV-2 ELISA identified 12 reactive serum samples (0.70%) and 1711 non-reactive (99.30%). Western blot analysis of the 12 ELISA-reactive samples confirmed two positive samples (16.67%), 4 negative (33.33%) and 6 indeterminate (50%). Positive samples reacted against the p16, p26, gp36, p53, p56, p68 and gp105 proteins. All 12 ELISA-reactive samples belonged to the HIV-1 Western blot indeterminate group. The two HIV-2-positive samples showed well defined reactivity to gp160, p53, p55 and p34 of HIV-1. HIV-1 seroconversion was observed in all 10 remaining samples during serological followup. CONCLUSIONS Two new HIV-2 seropositive cases were diagnosed using DAVIH-VIH-2 and HIV-2 Western blot in indeterminate HIV-1 Western blot samples. Results support the recommendation that HIV-2 Western blot be included in the diagnostic algorithm for HIV-1/2 to followup negative or indeterminate HIV-1 Western blot results. KEYWORDS Diagnosis, laboratory techniques and procedures, antibodies, HIV-2, Western blot, enzyme-linked immunosorbent assay, algorithm, Cuba.