The mydriasis provocative test with 1% cyclopentolate (CPT) was performed on 431 eyes with suspected or untreated open-angle glaucoma. Tonography was performed both before and during CPT to study the changes in aqueous dynamics during the test. Statistical analysis of the results yielded the following mean trends and correlations at a highly significant level (P less than 0.001) in the alterations: Intraocular pressure (IOP) rose (deltaP +/- SD) (+ 1.4 +/- 2.9 mmHg) and aqueous outflow facility decreased (deltaC) (-10%) during CPT. The distribution of deltaP and deltaC did not follow the normal Gaussian distribution. The change in deltaP deviated from the Gaussian distribution in 5-10% of the eyes. The deviating values concur with those of the responder eyes in which IOP rose greater than or equal to 8 mmHg during CPT. deltaP was linearly dependent on the initial IOP level Po and the absolute change was always almost constant, approximately +1.4 mmHg. Both the total series and the responder eyes displayed the same trend for the change in aqueous outflow facility in relation to the initial C value (Co): low Co values changed less on average and high Co values changed more and diminished. It is not known why the deltaC change was different depending on the Co value. The change in IOP correlated statistically highly significantly in the initial C value (Co). The loqwe the Co value, the higher was the mean IOP elevation during CPT. In contrast, the change in aqueous outflow (deltaC) did not corrrelate (N.S.) with the initial IOP level (Po) before CPT.