Thirty-seven aphasic patients whose native language is Spanish were divided into jbur groups: (1) Broca's, (2) Wernicke's, (3) Conduction, and (4) Anomia. Phonological errors produced on repetition and object-naming tasks were analyzed in terms of type of transJbrmation and degree of similarity between target and errors in terms of shared distinctive features. Segmental transformations were of the following types: (1)pure substitution, (2)pure addition, (3) deletion, (4) reduplicative addition (doublet creation)--anticipatory (right to left) or perseverative (left to right), (5) reduplicative substitution (doublet creation)--anticipatory or perseverative, and (6) mutual exchanges. Pure substitutions were the most prevalent, exchanges, the least. Some error O'pes were found to differentiate significantly between aphasic populations. We suggest that different mechanisms may underlie the same error type for different aphasic populations