Kenaf (Hibiscus cannabinus L.) is an annual fibre crop which is being studied as a potential source of paper pulp. The effect of water supply upon yield has been studied in the central area of the lberian peninsula, where water resources are scarce and water economy is highly desirable. Field experiments were carried out during 1989-1992. Irrigation treatments provided 100, 50 and 25% of the maximum evapotranspirated water. Maximum stem yield was 20 t dry matter per hectare. Results show that stem yields in the least irrigated plots were 40-50% of those obtained in the best watered treatment. Yield was not affected by the growth stage at which water stress occurred. On the other hand a decrease (3.2-degrees-C) of the mean temperature during the growth cycle was responsible for important reductions (55%) in final yield. Ninety five per cent of the incident radiation was intercepted when the leaf area index reached 4.1 cm2 . cm-2. Radiation use efficiency (RUE) of kenaf (cv. ''EL Salvador''), under near optimal growth conditions, was determined as 2.45 g . MJ-1. RUE was not much affected by temperature and variable amounts of total solar radiation.