A thorough study was performed on physical work capacity (PWC) of 135 males from the Bulgarian Air Force, aged 18 to 59 years. VO2max was measured directly by means of maximum cycle ergometry testing. The following mean values were obtained: 2.94, 3.03, 3.18 and 2.78 l.min-1 for the age groups 18-25, 35-40, 41-50 and above 50 years, respectively. The relative VO2max mean values per kg BW for the above age groups were 46.15, 35.89, 39.57 and 34.15 ml.kg-1.min-1, respectively. The obtained data, even though not definitive, helped to develop standards for the evaluation of the physical work capacity of pilots. Comparison of our results with those of Bulgarian and foreign investigators has shown that the PWC of Bulgarian pilots is greater than the PWC of some heavy physical workers. It is similar to the norms of Andersen /1/ and Shvartz and Reibold /2/. In accordance the PWC of Bulgarian pilots below 29 years old and 40-49 years old is greater than the working norms for US Air Force personnel. For unknown reasons, the PWC of pilots 35-40 years old is lower than the generally accepted norms for this age group. Testing of the PWC of air force personnel has two general aeromedical goals--establishment of the cardiovascular fitness level and establishment of a baseline for comparison and improvement of PWC by implementation of physical fitness training programs. In the last few years a thorough study was carried out at the Bulgarian Institute of Aviation Medicine for determination of the PWC of Bulgarian Air Force personnel.(ABSTRACT TRUNCATED AT 250 WORDS)