There is no standardized method for the assessment of physical activity, so it is important to investigate the validity and the comparability of different measures. In the first survey (1984/85) of the MONICA Augsburg project of the World Health Organisation (WHO), physical activity was determined by two different methods, an interview and a seven-day activity diary, and these are compared in this analysis. In the first MONICA Augsburg survey 2023 men and 1999 women participated (overall response 80.0% men and 78.7% women). The seven-day activity diary was completed only by men of the age group 45 to 64 years (overall response 62.2%). On the assumption that the seven-day activity diary is an instrument of proven validity, the interview was validated against this reference method in men aged 45-64 years. Activity scores for occupational and leisure time physical activity were formed by means of the data from the seven-day diary. Participants were classified as active or inactive, by using energy expenditure during work as an estimate for occupational physical activity, and duration of sport as an estimate for leisure time physical activity. The interview offered four possibilities for answering the activity questions. By means of these answers the participants were again classified into active and inactive groups, for both leisure time and occupational physical activity. This grouping was compared to the one obtained by the reference diary method. Validity of the interview-based scores required an efficiency of at least 160% and an error rate not above 20%.(ABSTRACT TRUNCATED AT 250 WORDS)