Cotton irrigation studies from 1988-1999, which included different irrigation scheduling methods at Lubbock, TX, used amounts of water that ranged from deficit to excessive amounts for maximizing lint yield. Scheduling treatments based on canopy temperature were included each year. Drip irrigation and recommended production practices for the area were used. This 12-year data base was analyzed to estimate the effect of irrigation and growing season temperature on yield. Yields in the irrigation studies were then compared with those for the northwest Texas production region. Maximum yield was estimated to occur at an irrigation input of 58 cm or a total water application of 74 cm. The components of total water supply for the maximum yield treatments averaged 74% irrigation and 26% rain. Lint yield response to irrigation up to the point of maximum yield was approximated as 11.4 kg/ha-cm of irrigation between the limits of 5 cm and 54 cm with observed lint yields ranging from 855 to 1608 kg/ha. The intra-year maximum yield treatments were not limited by water input, and the inter-year range of 300 kg/ha was not correlated with the quantity of applied water. The maximum lint yields were linearly related to monthly and seasonal heat units (DD60s) with regressions for July and August and from May to September being significant. The fluctuation of maximum lint yields and the response to DD60s was similar in the irrigation studies and the production region surrounding Lubbock. The rate of lint yield increase with heat units was slightly higher in the irrigation studies and is attributed to lower water stress in these treatments compared to the irrigated fields in the surrounding area.