The line Nantais Oblong, a melon of Charentais type, was shown to be a source of resistance by antibiosis to the leafminer, Liriomyza trifolii (Burgess), Diptera, Agromyzidae. We studied the genetic control of this resistance in F2 and back-cross progenies from the cross between Nantais Oblong and Védrantais, a Charentais line susceptible to the leafminer. Tests were carried out on young plants in plastic cages with controlled infestation. Complete mortality of the L. trifolii larvae was used as indicator of plant resistance. Segregation ratios were consistent with monogenic dominant control of the resistance. The symbol Lt for Liriomyza trifolii resistance is proposed.