Lathyrus odoratus has been classical material for genetic study ever since the rediscovery of Mendel's work. But up to now, no chromosomal aberrations of any kind have ever been found. The sweet pea, in common with all other species of Lathyrus hitherto investigated, has seven regular bivalents at meiosis. It is therefore of interest to report here the first discovery of tetraploidy in this plant.