91 strains of Vibrio cholerae O1, isolated in Bangladesh in January 1986, were examined for their biological behaviour and sensitivity to 6 antimicrobial agents. Biotyping indicated that 60 of the isolates belonged to the classical biotype and 31 to the El Tor biotype. 21 El Tor strains revealed beta-haemolysis on blood agar plates, but only 8 showed complete haemolysis in broth. Serotyping indicated 79 Ogawa, 10 Inaba, and 2 Hikojima. Phage typing showed that all classical vibrios belonged to Mukerjee's phage type 1. El Tor vibrios were classified into 4 groups: one strain each in type 1 and type 5, 19 in type 4, and 10 in an untypable group. Prophage typing of El Tor vibrios identified 14 strains of Ubol type, 16 of cured Celebes type, and one of original Celebes type. No strain was resistant to tetracycline, minocycline, chloramphenicol, streptomycin, amoxicillin or nalidixic acid. The classical vibrios differed from those isolated before 1973 in toxin production pattern.