As the third report on studies of nitrogen nutrition for muskmelon, this report deals with the results of experiment to clarify the influence of increased potassium concentration in nutrient solution upon the growth of melon and the absorption and assimilation of two forms of nitrogen, NH_4-N and NO_3-N, in the tissue of it. The results can be summarized as follows. 1. The growth of melon was remarkably affected by potassium deficiency. Especially, when NH_4-N was, instead of NO_3-N, supplied as a sole nitrogen source, potassium deficiency lowered the growth of melon, even if it had high potassium content. 2. The melons of AK_<100> were, in spite of their maximum growth among the AK-series, far less in their growth than those of NK_0 which had revealed potassium deficiency. This fact indicates that the melons of AK-series were affected on their growth by absorbing NH_4^+. 3. Owing to the fact that AK-series was having less base content in total and had comparatively less the amount of absorption of mineral nutrient than that of NK-series, it was indicated that the absorption of mineral nutrients was more remarkably affected by either NH_4-N or NO_3-N of the nitrogen form than the potassium concentration supplied. 4. Potassium deficiency caused accumulation of water soluble organic nitrogen together with glutamine in high level in the melons of AK-series, however, it was recognized that increased potassium lowered on the one hand the content of water soluble organic nitrogen to some extent, and on the other, as yet caused considerably high content of glutamine. This fact indicates that protein synthesis was retarded in the melons of AK-series. 5. Since the content of reduced sugar, non-reduced sugar and crude starch in the melons of AK-series was higher than that of NK-series, it can be understood that the growth of the one was more lowered than that of the other owing to the fact that they were retarded in their digestion by NH_4^+ and the supply of energy and carbon skeleton was restricted.