Hahn＇s New Pseudoisochromatic Colour Vision Test contains provision for screening red-green and blue-yellow colour vision deficiencies, a qualitative diagnosis as protan and deutan, and a quantitative diagnosis of red-green deficiencies. In this study 58 colour vision deficient and 68 colour vision normal subjects were examined using a battery of colour vision rests. The screening and classification ability of the Hahn test was compared with Ishihara＇s Test and the Standard Pseudoisochromatic Plates (SPP), The quantitative diagnosis ability was assessed by comparison with the Farnsworth-Munsell D-15 Test, the Farnsworth Lantern, and the Anomaloscope range. The Hahn proved to have a colour vision screening performance comparable with the two other PIC tests. Its classification ability was poor compared with the other PIC tests, one design in the SPP plates was markedly superior. The Hahn＇s quantitative diagnosis plates did not produce a useful classification; more than 50% of subjects made the full six errors and only 3 of 58 colour vision deficient subjects made less than 3 errors out of the 6 plates. The colorimetric measurements are used to illustrate the design features and are consistent with these performances.