G EEOGRAPHICAL and climatological literature abounds with references to the stress, temperateness, or intemperateness of climates. Most of these generalizations are qualitative, subjective statements, not based on concise criteria defining the constituent elements or describing how they could be mapped.' This study proposes a quantitative approach to the problem of climatic stress by introducing three annual indices: annual Cumulative Stress (CS), which measures the cumulative relative variations and departures from the human state of comfort; Proportional Cumulative Stress (PCS), which measures on an annual basis the percentage of heat stress in relation to cold stress; and Annual Physioclimatic Regime (APR), which attempts to synthesize the annual march of physiological climates, their regionalization, and their degree of fluctuation and frequency. The last classification also indicates the possible sources and causes of the various stresses as exhibited in the other indices. All these indices are applied to the United States, including Alaska and Hawaii.