We evaluated the Oculab Tono-Pen for potential value in the measurement of diurnal intraocular pressure. Repeated recordings every ten minutes on the same eyes suggested that the instrument provides reproducible information. However, comparisons with Goldmann applanation tonometric measurements, in both single determinations and eight-hour diurnal recordings, showed considerable variation. Correction factors, using either the mean difference in paired readings from the single measurement study or individual differences from the initial set of diurnal recordings, did not eliminate this lack of correlation between measurements with the two instruments.