SUMMARYSixteen isolates ofPhytophthorafrom cacao in 10 countries were compared for cultural, morphological, physiological, and biochemical characters. Twelve isolates were“typical”ofP. palmivoraand four were“atypical.”The typical isolates had a characteristic stellate pattern on carrot agar while the atypical isolates produced profuse aerial mycelium with no distinct pattern. Elongate, caducous sporangia tapering to the base, with long pedicels attached to the often flat bases were formed by the atypical isolates in contrast to the ovoid, caducous sporangia with short pedicels attached to the round bases produced by the typical isolates. Chlamydospores were formed by the typical but not the atypical isolates. The atypical isolates grew at 9 C on semisynthetic agar medium whereas the typical isolates did not. Two types of electrophoretic protein-band patterns were detected among the 16 isolates; one type was common to the atypical isolates and the other to the typical isolates. The typical isolates correspond to Morphological Form 1 ofP. palmivoraand the atypical isolates to Morphological Form 4. The atypical group of isolates may represent a species distinct fromP. palmivora.