The effects of moisture stress on leaf water potential ('ť|eaf)> photosynthetic rate (/^n) and stomatal resistance (r^) of cotton, Gossypium hirsutum L., were studied under field conditions. Sprinkler irrigation trials were conducted using the single source line technique. r^ increased and decreased as a result of moisture stress, more than in a concurrent drip irrigation experiment, r^ was only slightly affected by irradiance when the plants were subjected to moisture stress, but it decreased in response to an increase in irradiance (/) in the well irrigated plants. A linear relationship between T^ieaf and r^ and between 'ťigaf and found in both experiments at low /, whereas exponential relationship was found at high I. Even though high values of r^ were recorded under the extreme moisture stresses of both experiments, intemal CO2 concentration (cj) increased during the day, indicating that non-stomatal factors (such as mesophyll resistance) are the main factors limiting the photosynthetic process.