The respiratory rate, ethylene production and ripening of mature ‘Hass’ avocado fruits (Persea americana Mill.) were determined at 20° to 40°C. Typical climacteric patterns occurred at 20°, 25°, 30° and 35° with the climacteric maximum increasing with temperature, but only a decreasing respiratory rate with time was observed at 40°. Maximum ethylene production decreased as the temperature increased, with a significant decrease between 25° and 30°, only trace amounts were produced at 35° and essentially no ethylene production was detected at 40°. The ripened fruit quality was excellent at 20°, 25° and 30°, fair at 35° and abnormal and unacceptable at 40°. Fruit held at 40° for up to 2 days resumed ripening when transferred to 20°. The exposure to exogenous ethylene or propylene hastened the ripening response up to 35°, however at 40° the respiratory rate was increased, but ethylene production and normal ripening did not occur.