Bibliography: pages 191-202. / The surface heat balance of the Benguela upwelling area on the west coast of southern Africa is analysed. Measurements of the components of the heat balance were made in the St Helena Bay area from 14-21 October 1986. Additional long-term data was obtained from Alexander Bay and Cape Town. An average net heat gain of 227 W.m⁻² was received over the eight days of the field study. The presence of cold water determined that latent heat loss by the sea surface was small, while the sensible heat flux represented a small gain by the sea. These two turbulent heat fluxes are roughly equal and opposite and therefore approximately cancel each other. Use of a model, assuming idealised conditions, indicated that most turbulent heat exchange between the air and takes place in the nearshore region where air-sea contrasts are greatest. The net radiation was found to provide a good estimate of the total heat balance, thus the major contributing term to a high heat balance over the Benguela area is the input solar radiation. Minimal synoptic variation in the heat balance during the eight-day field programme was observed, but additional global radiation data analysed revealed that synoptic variations over the 3-6 day period are in fact more significant than the longer term seasonal variations. Both synoptic and seasonal variations in the heat balance are greater in the south than in the north. The high heat flux into the sea surface is capable of increasing the temperature of the upwelled water at a fairly rapid rate. During summer the heat exchange is capable of increasing the temperature of the upper 10 m mixed layer by as much as 0.65°C over one day. This input heat is used to realise the high biological potential of the upwelled waters.