A self-paced serial reaction task was developed to differentiate between the effects of intralaminar thalamic lesions on sensory attention and intentional motor function. Results were compared for hippocampal and frontal cortical lesions to test for the possible involvement of pathways involving these parts of the brain in any impairments associated with the thalamic lesion. Lesions of the intralaminar thalamic nuclei affected response latency without affecting accuracy. This increase in latency was unaffected by variations in stimulus duration, even though this manipulation had a substantial effect on response accuracy. Intralaminar lesions did not affect the response to distracting stimuli or to manipulations of stimulus salience. Thus it seems unlikely that the effects of intralaminar lesions on motor function were related to sensory loss or attentional dysfunction. Hippocampal lesions had no significant effect on any measure of performance. Frontal cortical lesions were associated with an increase in latency comparable to the intralaminar group and also affected the accuracy of responding to brief stimuli or under conditions of reduced stimulus salience. These results are discussed in light of evidence that lesions of the intralaminar nuclei affect functions mediated by anatomically related areas of frontal cortex and striatum.