The present report provides the first detailed description of the hippocampus in the Shaking Rat Kawasaki (SRK) mutant by using a panel of antibody markers to delineate its laminar organization. The mutant was characterised at postnatal day 21 by severe malformations of both neuronal position and orientation, the most striking of which was the presence of a rounded central granule cell mass in the dentate gyrus rather than the normal V-shaped granule cell layer. Despite this finding, the SRK dentate gyrus not only retained a cell-sparse molecular layer (thinner but similar in gross appearance to that of control littermates), but the sharp laminar boundary between its inner and outer parts was as clearly marked by IM1 and OM4 antibody staining as it was in the normal dentate gyrus. These immunocytochemical data suggest that the entorhinal terminal field of the dentate gyrus may be relatively normal in the mutant, despite entorhinal afferents appearing to take an abnormal trajectory after they fail to cross the hippocampal fissure. Laminar malformations included disruption of the SRK pyramidal cell layer, with spreading of the CA3 mossy fibre projection to an ectopic infrapyramidal position, radial displacement of CA1 pyramids, and transposition of a hitherto unremarked longitudinal fibre bundle immunoreactive for calretinin from its normal position in the stratum lacunosum-moleculare of field CA2 to an alvear position in SRK. The SRK malformations were very like but not identical to those seen in the mouse reeler mutant, suggesting similar underlying developmental mechanisms.