Measurements of small variations in 'absolute' pitch.

1. Longitudinal studies on absolute pitch estimates have been observed in one male and two female subjects.2. The female subjects underwent rhythmic variations in their estimates that were related to their menstrual cycles. One female subject, the more intensively studied of the two, also showed variations in her pitch estimates that were related to illness.3. Relevant correlations between the menstrual cycle and known biochemical parameters are mentioned which suggest that the fluctuations in the female estimates are governed by changes in the electrical activity of the auditory nervous system.4. The male subject showed similar fluctuations in his pitch estimates. A rhythm of approximately 20 days was observed.5. A connexion between the fluctuations in the pitch estimates and the sex hormones in both the female and the male subjects is suggested as a possible explanation of the difference between two different types of absolute pitch.6. The hypothesis is extended to show how the adrenal corticosteroids could account for the changes in the pitch estimates that occurred with illness.