Three Lathyrus sativus accessions were screened for their reaction to Mycosphaerella pinodes infection. Accession ATC 80878 displayed the lowest percentage stem lesion values (%SL) and was significantly more resistant to M. pinodes than ATC 80407 and ATC 80053. Accession ATC 80407 was the most susceptible, displaying the severest disease symptoms. A backcross and an F₂ population were generated using accessions ATC 80878 and ATC 80407 as the resistant and susceptible parents, respectively. The backcross and F₂ progeny segregated in a 3 : 1 and 7 : 9 ratio, respectively, for resistance/susceptibility, using the 99% confidence intervals for the means of the parental controls in each assay to determine the point of discontinuity. The segregation data from both populations fitted a Mendelian segregation model that suggested that resistance in the L. sativus accession ATC 80878 may be controlled by 2 independently segregating genes, operating in a complementary epistatic manner.