To examine whether certain aspects of the environment can have a significant effect upon the steady-state water content of hydrogel contact lenses during normal wear, nine volunteers monitored ambient temperature, ambient humidity, and the water content of their contact lenses over a 5-day period of daily lens wear. Three subjects wore Hydron zero-6 lenses (38% nominal water content), three wore Hydrocurve II lenses (55%), and three wore Permalens contact lenses (71%). The results indicate that a knowledge of ambient temperature and humidity is of little value in predicting the water content of hydrogel lenses under normal wearing conditions, at least with respect to the range of environmental conditions encountered in the course of this experiment