The present study evaluates the regional water content of clear and cataractous human lenses. In order to determine the lens water, a freeze-drying technique was used which leaves behind only a very small amount of residual humidity. The effectiveness of freeze-drying was demonstrated in experiments with animal eye lenses (rat, pig, bovine). The results obtained revealed that, like in other mammalian lenses, the human lens cortex exhibits a significantly higher overall water content than the nucleus. This pattern was found in clear lenses as well as in lenses with early 'senile' cataracts. Subcapsulary cataracts present a unique feature as in these lenses the cortical water content is enhanced while the fresh lens weight is significantly reduced. Observations of postmortem human eye lenses indicate that regional differences in water content are greatly abolished 24-48 h after death.