Frequencies of red-green blindness among Central Thais and Southern Chinese average 5,5%. No significant differences were detected between the communities regarding the overall rates of colourblindness or the distribution of specific alleles. Deutan: protan ratio is 2.4, the commonest defect being deuteranopia. Dichro-macies are commoner than anomalous trichromaeies. The combined rates of di-chromacies among Thais and Chinese are higher than among Japanese and Europeans. Discrepancies with results of previous surveys of the same populations are discussed, and the essentiality of anomaloscopy is stressed.