Close structural resemblances between several mammalian highly or moderately repetitive families and some specific tRNAs were detected. The rodent type 2 Alu family, rat identifier (ID) sequences, rabbit C family, and bovine or goat 73-bp repeat are most homologous with lysine tRNA5, phenylalanine tRNA, glycine tRNA, and glycine tRNA, respectively. The homologies extend to secondary structures, and the homologous nucleotides are located on nearly the same secondary structures. The repetitive families mentioned have a common structural organization, with a tRNA-like sequence devoid of an aminoacyl stem region. These features suggest that these repetitive families may be generated by nonhomologous recombination between a tRNA gene and a tRNA-unrelated block.