In contrast to the simplified, unvarying, and rigidly controlled conditions that characterize laboratory studies of human responses to cold, normal work in cold regions is characterized by a complex and unstable thermal environment, intermittent cold exposure and exercise, and the freedom to adjust clothing and activity for comfort. These "ergonomic" aspects profoundly modify the impact of a cold environment on people's health, comfort, and performance. A review of recent field studies in the Antarctic shows that the supposed "tropical microclimate" of clothed people in the cold is an over-simplification. People tend to be alternately chilled and overheated, and the accompanying exercise of the vascular responses provides a potential stimulus for vasomotor adaptation. Significant and substantial changes in men's responses to standardized whole-body cold exposures, observed on eight Antarctic expeditions, show that general acclimatization to cold develops as an increase in tissue insulation, which is mediated by an enhanced vascular response to cold.