Three-year-old nectarine trees of the cultivar Independence grown in free-drainage lysimeters were exposed to a wet and a dry treatment, i.e. high soil moisture content throughout or progressive soil drying respectively. The canopy temperature of the trees was measured with an infrared thermometer at midday. Leaf diffusion resistance (RL) and plant water potential (WP) were determined at the same time. Environmental conditions had an overriding effect on canopy temeperature. Water stress index (SI) and canopy temperature difference between the dry and wet treatment (CTD dry-wet) were therefore calculated. Stepwise multiple linear regression analysis indicated close correlation between SI or CTD (dry-wet) and WP and it was established that the effect of environmental conditions on SI and CTD dry-wet was unimportant.S. Afr. J. Plant Soil1986, 3: 110–114