Six hundred and twenty-four Vibrio cholerae O1 strains, 623 serotype Ogawa and one serotype Inaba, isolated in Romania between 1977–95 were tested to detect all changing traits concerning serogroup, serotype, biotype, phage type and resistotype patterns and subsequently, the possible epidemiological relationship among these strains. Biotyping revealed one classical, 580 eltor strains and 43 intermediary variants. When tested with Mukerjee phages, 546 (87%) strains were sensitive and 78 (13%) resistant. One phage type (M4) dominated during 1977–90, two phage types (M4 and M5) exhibited the same high frequencies during 1991, a diversity of types occurred during 1993–4 whereas in 1995, two phage types (M4 and M5) showed similar distributions again. Five patterns of drug susceptibility were successively described during 1977–95. The most prominent changes in Vibrio cholerae O1 strains were noticed during 1993–4: the highest number of non-typable strains and intermediary variants, the widest spectrum of phage types and of multidrug resistance. In 1995, the strains reverted to the previous typable forms but a new drug resistance pattern was noticed.