A serious cotton (Gossypium Hirsutum L.) plant disorder, temporarily called cotton "Leafburn", occurred in the Imperial Valley of California during July and August of 1989. All of 11 cotton types observed exhibited symptoms. Irrigation frequency in July did not appear related to the occurrence of "Leafburn". "Leafburn" symptoms were not visibly evident in portions of commercial cotton fields treated with aldicarb, while plants in untreated portions of the fields showed distinct "Leafburn" symptoms. Cotton yields averaged 2.5 and 0.7 bales/AC in aldicarb-treated and untreated portions of the fields. Leaves with "Leafburn" symptoms were under moisture stress as evidenced by lower leaf water potential, leaf conductance and leaf transpiration, and higher leaf temperatures. Data on environmental elements such as weather, air quality including forest fire ash residues, and quality of irrigation water were obtained and examined as possible causes of the "Leafburn" syndrome. Hypotheses were formulated regarding the problem and are discussed.