A program of laboratory studies into thermal comfort requirements is presented. Two studies used groups of 16 subjects over a range of conditions (warm to cool) to investigate the effects of gender over 3 h exposures in simulated living room/office environments. It was found that for identical levels of clothing and activity, there were only small differences in the thermal comfort responses of male and female subjects for neutral and slightly warm conditions. For cool conditions, female subjects tended to be cooler than males. An experiment to investigate the effects of heat acclimation on thermal comfort requirements involved six male subjects providing thermal comfort responses in neutral and slightly warm environments over 2 days. They then carried out an acclimatization program over 4 days, for 2 h per day, exercising in a hot (45 degreesC, 40% relative humidity) environment. Thermal comfort responses were then recorded in two sessions over 2 days in identical conditions to the pre-acclimation session. It was found that changes in thermal comfort responses were small and likely to be of little practical significance. An investigation into the behavior of people to maintain thermal comfort by adjusting their clothing was conducted using eight male and eight female subjects. Seated subjects reduced or increased their clothing level by using a wardrobe of clothing that was familiar to them. It was found that subjects can adjust their clothing to maintain thermal comfort, but within limits. Upper limits (clothing off) will be determined by modesty and acceptability. Lower limits (clothing on) will be determined by clothing design and acceptability. A low air temperature limit of 18 C in freely available clothing may provide a working hypothesis. A laboratory study of thermal comfort requirements for people with physical disabilities compared responses with those of people without physical disabilities. It was found that there are few group differences between thermal comfort requirements of people with and without physical disabilities. However, there is a greater necessity to consider individual requirements for people with physical disability.