We used a polarographic oxygen sensor to measure corneal oxygen uptake rates of 16 subjects during daily wear of soft contact lenses. The subjects reported for examinations on nine occasions over a 30-week lens wearing period. Corneal oxygen uptake rates were measured immediately after lens removal and at 11 additional times over the following 60 minutes. Compared to the pre-fitting (baseline) values, the oxygen uptake rate immediately after contact lens removal was substantially increased early in contact lens wear. It then fell in a nearly stepwise fashion over the 30-week observation period. Whenever measured during the 30-week course of the study oxygen uptake rate decreased rapidly over the first one to two minutes after lens removal. It then showed only minor fluctuations for the remainder of the 60-minute examination. At wearing durations longer than 19 weeks this stable oxygen uptake value was less than the baseline value. We suggest that these changes are a direct consequence of altered epithelial metabolic activity, although possible contributions from instrument drift and corneal thickness changes cannot be discounted.