Five new myelin basic protein (MBP) transcripts were identified which each have preferential sites of expression in adult human brain and immune system. They contain a novel 5' coding region which presents extensive sequence similarity to the mouse 0' region. One of these ribonucleic acid (RNA) species, HMBPR1, is found essentially, if not only, in haemopoietic and immune cells. Two alternatively spliced transcripts called MBP2a and c are only expressed in the central nervous system (CNS). In addition, the two other transcripts are expressed in both immune and nervous systems. Thus, the MBP locus can generate multiple forms of RNA, whose start sites and splicing depend on the tissue in which they are expressed. The presence of an MBP transcript specifically expressed in the adult human immune system suggests previously unsuspected functions related to the pathogenesis of multiple sclerosis.