Part of a beta -amylase genomic DNA sequence from the oomycete, Achlya bisexualis was cloned by polymerase chain reaction (PCR) using degenerate oligonucleotide primers derived from the conserved regions of other known beta -amylase sequences. The 5'- and 3'-regions of the beta -amylase gene were amplified by genome walking method. The Ach. bisexualis beta -amylase gene consisted of a 1338 bp open reading frame, encoding a protein of 446 amino acids with a molecular weight of 49 381 Da, and was not interrupted by any intron. The deduced amino acid sequence of the beta -amylase gene had 67% similarity to the beta -amylase of Saprolegnia ferax, followed by 40% similarity to that of Arabidopsis thaliana. The beta -amylase gene was expressed in Saccharomyces cerevisiae placing it under the control of the alcohol dehydrogenase gene (ADC1) promoter.