A group of 20 patients with probable Alzheimer disease (AD) and a control group were tested in a verb generation task, in a verb synonym task and several cognitive tests. Three types of verbs and novel verbs were presented in simple sentence frames, in two different conditions. In one condition participants were presented with the verb in the infinitive, providing information about the conjugation of the verb and the most likely type of past participle mapping required. The second was an ambiguous condition in which the suffix of the input verb did not provide any clue to the conjugation. The aim was to investigate if different types of verbs and input mapping affected patients' performance, and to what extent the deficit increased when the illness became more severe. Dependent measures were accuracy rates, rates of different morpho-phonological transformations and error type rates. Patients showed a more marked deficit in verb generation, when input was ambiguous. Correlation between the verb synonym test and accuracy in verb generation indicated that a deficit in lexical-semantic memory was partially responsible for impaired performance. Data suggest that patients maintained information about frequency distribution of different verb types and verb classes in each conjugation, but were impaired in operating complex phonological transformations.