Laboratory studies of the susceptibility to insecticides of the sugarcane borer, Diatraea saccharalis (F.), were conducted during 1962–63. A technique for testing borer susceptibility to insecticides in the laboratory was developed. Newly hatched larvae were exposed to residual films of insecticides in 125-ml Erlenmeyer flasks for from 30 minutes to 5 hours before being transferred to an artificial diet. During the late summer of 1963 a high level of resistance to endrin was demonstrated in the laboratory in the progeny of field-collected sugarcane borers from Port Allen, Louisiana, where satisfactory borer control had not been obtained by applications of endrin earlier in the summer. Low levels of approximately 2-fold tolerance to endrin were found also in strains from Baton Rouge, Franklin, and Meeker, Louisiana. The Port Allen strain, which was highly resistant to endrin, was found to be quite resistant to endosulfan also, thus exhibiting cross resistance. The endrin-resistant and susceptible strains were approximately equally susceptible to azinphosmethyl and carbaryl.