Recent studies have identified a number of new genes mapping to the class-II region of the human major histocompatibility complex. Functionally these can be grouped into three broad categories: those encoding the new class-II-related genes DMA and DMB; those involved in aspects of class-I antigen-processing and presentation, and those with no apparent association with the immune system. There is evidence that further factors involved in class-II antigen presentation are located in the DMB to DQB1 interval.