A bovine tRNA gene cluster has been characterized and the sequences of four tDNAs determined. Two of the tDNAs could encode tRNA(SerIGA), one tRNA(SerUGA), and the fourth tRNA(GlnCUG). The three serine tDNAs representing the UCN codon isoacceptor family are almost identical. However, the sequence of the tDNA(SerTGA) differs from a previously sequenced bovine tDNA(SerTGA) at 12 positions (ca. 14%). This finding suggests that in the bovine genome, two subfamilies of genes might encode tRNA(SerUGA). It also raises the possibility that new genes for a specific UCN isoacceptor might arise from the genes of a different isoacceptor, and could explain previously observed differences between species in the anticodons of coevolving pairs of tRNAs(SerUCN). The gene cluster also contains complete and partial copies, and fragments, of the BCS (bovine consensus sequence) SINE (short interspersed nuclear element) family, six examples of which were sequenced. Some of these elements occur in close proximity to two of the serine tDNAs.