Abstract : The effects of one tranquilizing and two analeptic drugs on the physical working capacity and on cardiovascular responses to postural changes were investigated. A definite increase in work capacity was observed after ingestion of a combined caffeine-metrazol preparation, apparently resulting from an increased capacity for cardiac output and maximum oxygen intake. Recordil, a relatively new Italian drug and a very potent dilator of coronary arteries, also improved work capacity but caused a tendency for orthostatic syncope probably due to its generally vasodilating effects. The blood pressure depression observed with Equanil (from the meprobamate group) during rest, exercise and tilting, especially with larger doses, raises the question about the safety of people engaged in the operation of aircraft or motor vehicles when 'sedated' by this drug. Serious incidents and fatal accidents may be precipitated by the emotional indifference to suddenly arising problems or as a consequency of delayed circulatory responses during flight maneuvers. (Author)