The frequency of colour blindness among the Jat males is 2.52% in Delhi and 4.53% in the Punjab. The difference between the Jats of the two areas is insignificant. The ratio protan (red blind) to deutan (green blind) type is 1:2.25 among the Jats of the Punjab, while all the affected males in Delhi were of the deutan type. The frequency of colour blindness among the Jats (Delhi and Punjab pooled together) is 3.53%. The protan:deutan ratio is 1:4. None of the females tested were found to be colour blind. The similarity of the Jats with most of the populations in North-Western India for the frequency of colour blindness indicates a considerable homogeneity in this region.