The drawings of 70 control subjects, 95 right and 118 left brain-damaged patients (BDP) were evaluated by two independent judges having no knowledge of the literature on constructional apraxia, who were requested to give both a quantitative and a qualitative evaluation of each drawing. Scoring made it possible to classify the BDP as affected or not affected by constructional apraxia. Qualitative errors were classified in two groups: (A) "executive" errors: increased number of right angles, structural simplification of the models and omission of details and (B) "visualspatial" errors: inattention to lateral elements or omission of one half of the figures, errors in spatial relations and diagonal orientation of the drawings. Contrary to expectations, no clear qualitative difference was observed between the drawing errors of right and left BDP. The types of errors most frequently observed in constructional apraxics were very similar, irrespective of lesion side, and consisted in difficulty in reproducing the spatial relations between the various parts of the models and in a tendency to oversimplify the most difficult designs. The only type of error which differentiated right apraxics from left apraxics was omission of lines or of whole figures on the half space contralateral to the damaged hemisphere, but this type of error could not be responsible for right-sided constructional apraxia, since judges had been instructed to base their assessment only on the parts of the models actually reproduced by the patients without scoring as errors manifestations of neglect. These results do not support the hypothesis that two different mechanisms, "executive", and "visual-spatial", underlie constructive disabilities of left and right brain-damaged patients.