We have recently published a new probabilistic algorithm which performs genomic comparisons on a huge scale. In the present paper it was applied to immunodeficiency viral sequences extracted from international gene databanks. During global sequence analysis of human (HIV1 and HIV2) and simian viruses by means of dot-matrix representation, series of homology were obtained which permitted the definition of families of viruses overlapping the species divisions. Sequences of interest were characterized to the lexical base sentence through successive zoomings. Strain-to-strain comparison confirmed subfamily classifications and led, for example, to the identification of divergent LTR sequences. By way of example, we described the application of the algorithm to the ANT70C and MVP5180 HIV1-O viruses, for which the observed differences were shown to correspond to a deletion in the U3 region, situated between the LEF and NF-kappaB sites. It was of interest to consider these data in a tentative phylogenetic interpretation.