The author investigated a number of illnesses for circannual periodicities in their onset & severity. Data was obtained for deaths due to asthma, bronchitis, ischemic heart disease, suicide & ulcer in Texas for the years 1980-86. Analysis substantiated statistically significant circannual variations of mortality in all categories except for deaths due to ulcers. However, the mechanisms underlying seasonal patterns of mortality are as yet undetermined. (21 refs.)