The possible involvement of stress-induced ethylene in softening of 'Saijo' persimmon fruit with or without>95% CO₂ treatment for 16 hr at 25°C, a technique widely used for the removal of astringency (Constant Temperature Short Duration (CTSD) method) was investigated. To confirm the role of ethylene in fruit softening, fruit were treated with 1-methylcyclopropene (MCP), a strong inhibitor of ethylene perception. The softening of treated fruit was inhibited markedly compared with non-treated fruit. Fruits, with or without CO₂ treatment, were held in high (>95% RH) or low humidity (40-60% RH) at 20°C to determine the effects of water and CO₂ stresses on postharvest ethylene production and fruit softening. Without CO₂ treatment, ethylene production and fruit softening were retarded significantly by high humidity. Whereas, with CO₂ treatment, a considerable amount of ethylene was produced and fruit softened, irrespective of humidity. These results indicate that ethylene is involved in fruit softening and that its evolution is stimulated not only by water stress but also by CO₂ stress in 'Saijo' persimmon fruit.