Bursaphelenchus xylophilus isolate MPSy-lav was subcultured from pathotype MPSy-1. MPSy-lav is nonparasitic and does not establish in Pinus sylvestris, P. strobus, P. nigra, or P. taeda. This isolate produces ethanol as an end product of carbohydrate metabolism, whereas its parent pathotype, MPSy-1, does not. Alcohol dehydrogenase activity was easily detectable in homogenates of MPSy-lav but barely detectable in some homogenates of MPSy-1. Genomic differences were seen between MPSy-1 and M PSy-lav by restriction endonuclease analysis of total nematode DNA, and hybridization of DNA fragments to the alcohol dehydrogenase gene from Drosophila. Key words: alcohol, alcohol dehydrogenase, Bursaphelenchus mucronatus, Bursaphelenchus xylophilus, metabolism, pathotype, pinewood nematode, Pinus sylvestris, P. strobus, P. nigra, P. taeda.