Retrograde axonal transport of horseradish peroxidase was used to identify the afferent projection systems of the anterior thalamic nuclei in the cat. The results indicate that fibres projecting to the three anterior nuclei of the thalamus arise from the hippocampal region, septum and cingulate cortex unilaterally and from the hypothalamus (mamillary nuclei) both bilaterally and unilaterally. The cells of the medial mamillary nuclei send their axons to the ipsilateral AV and AM nuclei whereas the lateral mamillary nucleus projects bilaterally to the AD nuclei.