The objective of this experiment was to determine the factors influencing the transpiration rates of mature, clonal tea (Camellia sinensis L.) and estimate its transpiration efficiency. The heat pulse technique was used to measure transpiration rates of tea plants growing in the field as part of extensive canopies at Talawakelle, Sri Lanka during the period between 1 January and 19 February 1997. Irrigation and shading treatments were used to determine the influence of soil water content (S) and irradiance on transpiration rate. The transpiration rate declined only slightly when S decreased from field capacity (44%) to 33%. However, when S declined below 33%, the transpiration rate showed a rapid decline from 1.6 to 0.7l per plant per day at 15% S. When S was near field capacity, maximum transpiration rates of 0.53–0.93l plant−1 h−1 occurred between 1000 and 1500h. The corresponding maxima when the S was near permanent wilting point (i.e. at −1.5MPa matric potential) were 0.27–0.53l plant−1 h−1. Transpiration decreased linearly with decreasing irradiance throughout the range of radiation levels tested (i.e. from 100 to 15% of full sunlight) at a rate of 0.031l per plant per day per % reduction in solar irradiance. The daily transpiration rates of tea plants (0.42–1.07l per plant per day) under the natural shade of Grevillea robusta were considerably lower than the value of tea plants in the open, 3.511l per plant per day. Spraying of an antitranspirant, Kaolin, decreased canopy temperature by 2–4°C and especially around mid-day. Kaolin also decreased transpiration slightly during the period between 1000 and 1500h. Transpiration efficiency (T E) was 9.637kgha−1 (made tea) mm−1 of water transpired. The relationship between total dry matter yield and the ratio between transpiration and mean saturation vapour pressure deficit also was linear with a proportionality constant of 6.9gkg−1 kPa.