The prefrontal cortex of the guinea pig was investigated in a search for afferents from cortical areas outside the frontal lobe using the horseradish peroxidase retrograde tracing technique. Based on afferents from the medial, the lateral, and from both parts of the thalamic mediodorsal nucleus, three prefrontal subregions were defined, namely the sulcal (within and above the rhinal sulcus), the medial (anterior and superior to the genu of the corpus callosum), and the fronto-polar subfield. Only the fronto-polar region was found to receive afferents from insular, cingulate, retrosplenial, parietal, and temporal cortical fields. Both of the other subfields received afferents only from neighboring cortical regions: the medial subfield from cingulate and retrosplenial areas and the sulcal subfield from the insular cortex. For all three subregions, the number of labeled cells was found to be small. These results were interpreted with caution, as extent and subdivisions of the guinea pig's prefrontal cortex and its comparability with that of other species depend considerably on the criteria used.