This study attempts to answer the question of whether there is a characteristic individuality of breathing pattern in conscious man. Measurements of breathing pattern, electroencephalograms and electrooculograms were made on 41 healthy individuals under standardised conditions of relaxed wakefulness, with a minimum of visual, auditory, and tactile input. Noninvasive measurement techniques were utilised and the subjects did not know that their breathing was being monitored. Measurement periods of only 5 min were used in order to avoid sleep. To estimate reproducibility, subjects were studied four times over two days. A variety of statistical tests on respiratory and cardiovascular variables indicate that the differences between individuals are highly significantly greater than the differences within an individual on repeated measurements under these standardised conditions. There was a high degree of reproducibility of breathing pattern within a subject; respiratory frequency was the most reproducible variable.