The effect of moisture on seed longevity during experimental storage was investigated in cucumber (Cucumis sativus L.), melon (Cucumis melo L.), and watermelon (Citrullus lanatus Matsum and Nakai). Seeds were stored hermetically at various moisture contents between 8.0 and 17.0% (fresh weight basis) at 35 degrees C for up to 215, 366, and 175 days for cucumber, melon, and watermelon, respectively. Normal germination percentages were determined periodically. A one-step approach was taken to analyze the effects of moisture on longevity and to estimate K-E and C-W. K-E and C-W values were found to be 4.86 and 1.59 for watermelon, 6.11 and 2.59 for melon, and 5.35 and 2.03 for cucumber, respectively. Watermelon seeds are the most sensitive to seed storage, whilst melon seeds have the greatest longevity. These constants can be used to predict the viability of these cucurbit seeds under various storage conditions.