Six New York State populations of Meloidogyne hapla differed in their reproductive fitness and severity of galling induced on lettuce (Lactuca sativa) cvs Ithaca, Salinas, and Montello and the breeding line 41-595. Both lettuce germplasm and nematode population had a significant effect on reproductive fitness and the interaction between germplasm and population was also significant. Differences in the number of nematodes recovered per g of root was attributable to differences in numbers of eggs per egg mass. Results suggested that there are separate genetic factors controlling reproduction and galling on lettuce. Based on this study, it would be prudent to include multiple, local populations of M. hapla in future resistance germplasm screening tests.