Sulfonylurea herbicide resistance was crossed into a susceptible (S) prickly lettuce biotype and into ‘Bibb’ (B), a domestic lettuce cultivar, and inheritance of the resistance trait was determined. The best fit for Chi Square analysis of the metsulfuron treated F2 generations was a 1:2:1 ratio indicating the trait was controlled by a single nuclear gene with incomplete dominance. F3 generations also were treated with metsulfuron. The F3 seedlings from resistant F2 plants were resistant while the F3 seedlings from intermediate F2 plants segregated.