A contig of cosmids containing the Ring1, Ring2, Ke6, Ke4, Rxrb, and Col11a2 genes in the rat major histocompatibility complex has been established and aligned to the class II cluster (RT1.Hb). The relative order and the transcriptional orientations of these rat genes are the same as in their human and mouse homologues. The distances are also similar, except for the Col11a2 - class II interval, which is clearly shorter in rat and mouse compared with human. The previously defined Ke5 probe could be shown to map into the large Col11a2 gene.