Measurements of central and peripheral corneal thickness, corneal topography and central corneal curvature were made for 21 subjects at hourly intervals for 12 h of 1 day for each [human] subject. Values for corneal radius and asphericity were obtained from keratometry and photokeratoscopy, and their stability throughout the days was evluated. Corneal radius steepened during the day; asphericity remained constant. Corneal thickness measured by pachometry was at its thickest on first awakening. Corneal curvature and central corneal thickness were highly correlated; low correlation was found between corneal asphericity and central corneal thickness. Some subjects exhibited large fluctuations in 1 or all of the parameters considered.