A comparison was made of three methods of bacteriological diagnosis during the outbreak of cholera due to Vibrio El Tor in the Republic of the Philippines in the last quarter of 1961. Although the disease was clinically indistinguishable from cholera caused by V. cholerae the etiological agent was a haemolytic, cholera-related vibrio which differed in some respects from what is classically regarded as V. cholerae. Of the three techniques evaluated, the selective-enrichment/fluorescent-antibody technique provided the most rapid and the greatest number of positive results in the 481 specimens examined in parallel. The oblique-light technique was second in sensitivity and rapidity, while the gelatin-agar method also had some advantages.