THE Rev protein of human immunodeficiency virus type I (HIV-1) facilitates the nuclear export of unspliced and partly spliced viral RNAs. Rev contains an RNA binding domain, required for interaction with HIV-1 RNA, and an effector domain, required for RNA-bound Rev to function. The Rev effector domain is believed to interact with a cellular cofactor required for the Rev response and thus HIV-1 replication(1,2). Here we report the use of a yeast two-hybrid screen to clone human Rev interacting protein (hRIP), which specifically interacts with the Rev effector domain. This hRIP protein has hemology with nucleoporins, a class of proteins that mediate nucleocytoplasmic transport(3,4). These and other properties of hRIP are those expected of a Rev cellular cofactor.