The genetics of resistance of several rice cultivars (Oryza saliva L.) to the brown planthopper, Nilaparvata o lugens (Stal), and to the green leafhopper, Nephotettix impicticeps (Ishihara), was studied in the greenhouse. Two testing techniques were developed and employed. In one, 7-day-old seedlings were infested with insects and then classified on the basis of insect injury. In the other a known number of insects were caged on tillers of 6-weekold plants and insect survival was used as the criterion for classification. The resistance of 'Mudgo,' 'Manavari CO22,' and 'Dalwa Sannam MTU15' to the brown planthopper was controlled by single dominant genes that appeared to be allelomorphic. Another cultivar, 'Karsamba Red ASD7,' possessed a single recessive gene for planthopper resistance that was either allelic or closely linked to the locus that conditions resistance in the other three cultivars. The field reaction of F 4 lines of a cross between Mudgo and a susceptible cultivar was strongly correlated with the greenhouse reaction, and aparently the same gene controlled planthopper resistance at different stages of growth. Resistance to the green leafhopper in the cultivars 'Pankhari 203,' 'ASD7,' and 'IR8' also was controlled by single genes that were nonallelic and dominant. The planthopper resistance of Mudgo, and the leafhopper resistance of Pankhari 203 were independently inherited as was the resistance of ASD7 to the two insects.

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