Charcoal rotor ashy stem blight caused by the soil-borne fungus Macrophominaphaseolina (Mp) is recognized as an important disease of bean (Phaseolus vulgaris) in Puerto Rico (PR) and the Dominican Republic (DR). Severe symptoms occur especially when bean seedlings or adult plants are stressed from moisture deficits. Differences in virulence and morphological, physiological, and biochemical characteristics were obtained among PR and DR isolates of Mp in this study. PRMp2 was more virulent than PRMpl. However, DRMp2 was more virulent than either PRMp2 or DRMpl. Mycelia morphological characteristics and sclerotia size were similar in the DR isolates but different from those of the PR isolate. There were not significant differences in sclerotia size and mycelia radial growth of each isolate under light or dark conditions. Analysis of protein patterns of the PR and DR isolates was performed by polyacrylamide gel electrophoresis (PAGE). Protein profiles of DR isolates were similar but different from that of PR isolate (PRMp2).