The in vivo wettability of soft contact lenses worn by a group of 10 subjects was monitored over a 24-hour period including 8 hours closed eye. Two types of lenses were tested: Igel 67 (Prima) and Bausch & Lomb 70. They were each worn once in both eyes by all the subjects. The in vivo wettability of the lenses tested was evaluated by measuring the pre-lens non-invasive break-up-time (NIBUT) and assessing the nature of the pre-lens tear film structure. The results obtained showed good wettability throughout the study and no difference between the two materials tested, but a significant difference between open and closed eye wear. The tear film was far more stable (p less than 0.01) immediately upon waking (mean NIBUT 21.2 s) than during open eye wear (mean NIBUT 11.2 s). Also at waking the pre-lens lipid layer was thicker than during open eye wear and the lens surface had a greater mucous coating. The presence of a more stable pre-lens tear film at waking was associated with a different tear film structure. We believe these differences in pre-lens tear film structure are responsible for the greater stability recorded.