Several field and sweet corn varietiea from several sources were crossed with a variety carrying the opaque-2 gene to determine the phenotypic interactions in the breeding of high lysine maize. Although opaque-2 lines showed lower protein content than the corresponding normal varieties, there was no correlation between the protein levels of the two types. opaque-2 maize contained more lysine, but no relationship was found between the protein content and the lysine content of either normal or opaque-2 types, suggesting that high lysine corn using the opaque-2 gene may be developed independently from the protein content. The F2 segregation ratios for normal and opaque-2, 100-kernel weights, percentage seed set, opaque-2 phenotype, disease susceptibility, and the relationship between protein and lysine content of normal and opaque-2 were investigated. The determinations and observations were made on the F2, F3, and BC1 Lysine content was determined by the ion exchangeresin combined with paper chromatography method. Most crosses segregated in a 1-opaque-2 : 3-normal ratio as expected. Opaque-2 segregates were lighter than the normal type and smaller in size. A mottled phenotype of opaque-2 maize observed in the Philippines yellow endersperm. In some varieties opaque-2 maize was very susceptible to the ear and kernel rot disease. No. 5(female) and opaque-2(male). Selectlon of a double mutant of waxy and opaque-2 by using the iodine technique and electric lamp was discussed. opaque-2 and floruy-2 were not allels. Different percentage of seed set were observed in the segregation of aewx crossed with opaque-2. An unusual gametophytie relationship was involved in a cross between Glutinous.