Water is the most limiting factor in cotton production, and numerous efforts have been made to improve crop drought tolerance. Field studies were conducted in 1998 and 1999 to determine if foliar application of glycine betaine would enhance yield in cotton under both drought and irrigated conditions. In 1998, glycine betaine treated plants had numerically, but not significantly (P=0.05) greater boll numbers, boll weights and lint yields. In 1999, yields were inconsistent, with glycine betaine generally having no effect. No differences in photosynthetic rate between treated and untreated plants were encountered either year of the study. In 1999, plant water relation trends suggested that glycine betaine might assist in osmotic adjustment.