A method of quantifying the combined amount of an HIV-1 M group nucleic acid and an HIV-1 O group nucleic acid that may be present in a biological sample, comprising the steps of: (i) combining in a single reaction vessel said biological sample, a first amplification primer wherein said first amplification primer comprises a target hybridizing sequence consisting of SEQ ID NO: 15, a second amplification primer, and a hybridization probe; (ii) amplifying with substantially equal efficiency any of the HIV-1 M group nucleic acid and the HIV-1 O group nucleic acid present in the biological sample using an in vitro amplification reaction that comprises enzymatic extension of said first amplification primer using a first strand of said HIV-1 M group nucleic acid or said HIV-1 O group nucleic acid as a first template to create a first primer extension product, and enzymatic extension of said second amplification primer using said first primer extension product as a second template, whereby there are produced HIV-1 M group amplicons if the biological sample contained said HIV-1 M group nucleic acid, and HIV-1 O group amplicons if the biological sample contained said HIV-1 O group nucleic acid; (iii) monitoring amplicon production of said amplicons in said in vitro amplification reaction as a function of time by a process comprising detection of a signal from said hybridization probe, whereby time-dependent quantitative data is obtained; and (iv) quantifying the combined amount of said HIV-1 M group nucleic acid and said HIV-1 O group nucleic acid present in the biological sample using the time-dependent quantitative data obtained in the monitoring step, wherein neither said first amplification primer nor said second amplification primer is fully complementary to said HIV-1 M group nucleic acid or the complement thereof, or to said HIV-1 O group nucleic acid or the complement thereof, and wherein said hybridization probe hybridizes to both HIV-1 M group amplicons and HIV-1 O group amplicons. (i) combining in a single reaction vessel said biological sample, a first amplification primer wherein said first amplification primer comprises a target hybridizing sequence consisting of SEQ ID NO: 15, a second amplification primer, and a hybridization probe; (ii) amplifying with substantially equal efficiency any of the HIV-1 M group nucleic acid and the HIV-1 O group nucleic acid present in the biological sample using an in vitro amplification reaction that comprises enzymatic extension of said first amplification primer using a first strand of said HIV-1 M group nucleic acid or said HIV-1 O group nucleic acid as a first template to create a first primer extension product, and enzymatic extension of said second amplification primer using said first primer extension product as a second template, whereby there are produced HIV-1 M group amplicons if the biological sample contained said HIV-1 M group nucleic acid, and HIV-1 O group amplicons if the biological sample contained said HIV-1 O group nucleic acid; (iii) monitoring amplicon production of said amplicons in said in vitro amplification reaction as a function of time by a process comprising detection of a signal from said hybridization probe, whereby time-dependent quantitative data is obtained; and (iv) quantifying the combined amount of said HIV-1 M group nucleic acid and said HIV-1 O group nucleic acid present in the biological sample using the time-dependent quantitative data obtained in the monitoring step, <EOS>