Both the alpha- and beta-tubulin genes of Leishmania enriettii are encoded by mRNA of 2.0-2.2 kb in length. We have shown previously that the alpha- and beta-tubulin genes are arranged in separate, tandem repeats of 2 and 4 kb, respectively, and now report the mapping of mature mRNA onto these cloned genes. Here we show that the alpha-tubulin gene contains a very short intergenic region (100-200 bases) whereas the larger, tandemly repeated beta-tubulin gene contains a 1.8-2.0 kb region not found in mature mRNA. Comparison of S-1 mapping and primer extension results indicates that the messenger RNAs for both alpha- and beta-tubulin contain a sequence of about 35 base pairs located at the 5' end that is not encoded contiguously with the rest of the mRNA. This short 5' sequence may be added to the body of the tubulin mRNAs either through splicing of a precursor RNA molecule or by a novel post-transcriptional processing reaction. The alpha- and beta-tubulin genes are arranged identically in the two developmental stages of the parasite life cycle and are present in equal copy number.