The effects of exposing a group of 16 men to a combination of heat (35–40°C) and low-frequency (4–8Hz) mechanical vibration for short periods of time, were examined to detect possible interference with cardiovascular function and the Incidence of referred pain. In an attempt to elucidate the multi-factorial etiology of cardiovascular disease, a number of measures were studied, blood pressure, pulse rate, peripheral circulation as seen by infra-red photography, electrocardiographic changes of rhythm and form, plasma lipids and cholesterol, cardiac enzymes (LDH, CPK, SGOT) , differential blood counts, smoking, age, occupation and other personal habits. The results have also been used to study the contribution of transient exposure to heat and to vibration on cardiovascular function as indicated by biochemical and physiological changes usually associated with conditions of environmental stress. Some of the material has been extended to include differences in daily physical activity and occupational exposure to driving motorized vehicles but the material was Insufficient to allow firm conclusions. The main points of interest have been to establish particularly the use of infra-red photographs of peripheral vascular changes and changes in ECG as useful diagnostic indicators of response to environmental stress. These changes also suggest a close parallel with clinical and cardiovascular disease diagnosed by biochemical methods. The results also show a most interesting counter action between the effects of transient exposure to heat and vibration separately and simultaneously.