Pupil changes provide vital information related to the cause and location, and at times, severity of disease processes which alter level of consciousness. Size and reactivity are sensitive to a variety of influences including local eye damage, functional state of brainstem, local systemic drugs, seizures and anoxia. Therefore, accurate measurement of pupillary size and reactivity is essential. The purposes of this study were to determine if pairs of nurses (1) achieved the same measurement of pupil sizes with and without an objective measure, and (2) selected the same descriptor for pupillary reaction to light. Sixty-eight pairs of nurses employed in adult and pediatric units of a large teaching hospital participated in the study. Interrater reliability of pupillary assessment of 136 nurses was determined. There was no significant difference in the reliability of nurses assessing pupillary size regardless of whether they used a penlight pupil gauge to measure or used observation without a pupil gauge. Agreement among the nurses on the pupillary size was high. Agreement on the pupillary reaction, however, was poor to good.