During a study of the gene coding for alpha-galactosidase (EC 3.2.1.22), the lysosomal enzyme deficient in Fabry's disease, RT-PCR amplification of alpha-galactosidase mRNAs obtained from three different tissues isolated from males revealed a substantial number of clones with a U to A conversion at the nucleotide position 1187. Such a modification of the coding sequence would result in an amino acid substitution in the C-terminal region (Phe396Tyr) of the enzyme. Neither PCR analysis of the genomic sequence nor the RT-PCR amplification of RNA obtained by in vitro transcription of the wild-type cDNA showed this change in the sequence. Multiple genes, pseudogenes are allelic variants were excluded. Hence, we propose RNA editing as a mechanism responsible for this base change in the alpha-galactosidase RNA.