The Jones primary dye test is a commonly used test of lacrimal outflow. Some clinicians, however, find it of limited practical significance because of variable outcome and relatively low sensitivity in documenting normal lacrimal excretory function. We hypothesized that an important variable affecting the transit time may be the volume of fluorescein used in the primary dye test. To accurately determine the exact time from insertion of dye into the eye to its appearance in the nose, using a rigid nasal endoscope, we directly visualized the dye as it appeared at the ostium of the nasolacrimal duct. Fifty nasolacrimal outflow systems were examined in 25 normal volunteers. The fluorescein dye transit time was determined using a single drop of fluorescein on one side and multiple drops of fluorescein on the other side. Using a single drop of fluorescein, the median dye transit time was 8 min, compared to 1.4 min using multiple drops. These results suggest that the volume of fluorescein used may be an important factor affecting variability in the outcome of the primary dye test.