On the basis of significant sequence similarity, we have identified JmjC domains in more than 100 eukaryotic and bacterial sequences,These include human hairless, mutated in individuals with alopecia universalis, retinoblastoma-binding protein 2 and several putative chromatin-associated proteins. JmjC domains are predicted to be metalloenzymes that adopt the cupin fold, and are candidates for enzymes that regulate chromatin remodelling.