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The biological characteristics of 11 HIV-1 strains isolated from patients with a fast clinical evolution to AIDS were studied. The viral isolates were classified according to their replication kinetics and cell tropism. Taking into account these criteria, it was observed that 8 of the isolated strains (72.7%) were of rapid high growth (RH) or slow low 3 (SL3) with preferential tropism to the lymphocytic stock, as it corresponds to AIDS patients. 3 (27.3%) had characteristics of slow low 1 (SL1). The cytopathogenicity of the strains was studied in the MT4 cellular line, and it was observed that most of them (72.7%) were syncytium-inducing strains (SI), which allowed to prove the in vivo and in vitro relation of the biological properties. It was not so in 3 of the cultures (27.3%) that behaved as non-syncytium inducers.

The exoantigen test has been successfully used in the last years for the immunological identification of pathogenic fungi. Twenty seven straing presumptively identified as Histoplasma capsulatum by morphologic methods, were studied by such test. The exoantigens obtained from each strain were studied by immunoprecipitation technique in front of histoplasmosis control sera experimentally obtained in rabbits. Reference strains of Histoplasma capsulatum. Histoplasma duboisii and Paracoccidioides brasiliensis were used. Of the strains studied, 96% was identified as H. capsulatum by the exoantigen test, a simple, rapid and highly specific technique greatly useful in the laboratories of Microbiology.