The influence of potassium (K) on respiratory behavior, flesh firmness, and internal color of watermelon (Citrullus lanatus) was studied. Two cultivars (Crimson Sweet and Sangria) were planted at the Univ. of Florida research station, Gainesville. The fruits from both cultivars were harvested at two different stages of maturity (25 days and 35 days after anthesis). Respiration and ethylene production were measured using gas chromatography under a static system. The internal color was measured by a colorimeter, while the flesh and rind firmness were measured by a instron Universal pressure tester. Carbon dioxide and ethylene production were non-climacteric in behavior and were not greatly affected by K treatment or cultivar.