The colour mechanism sensitivities of three protanomals and three protanopes have been measured at various spectral points, in an attempt to describe some anomalies of increment threshold data in terms of interaction effects. The π2, secondary maximum is greatly reduced and the π1 inflexion apparently increased in both protanomals and protanopes. π5 has a sensitivity similar to that of π4, and π5′ has a spectral sensitivity different to that of π5 in prolanomaly; π5 and π5′ are lost in protanopia. The primary modes of the auxiliary blue mechanisms π1 and π2 are independent of π4 and π5, while the secondary mode of π2, seems to depend on the difference in gradient of π4 and π5. π4′ and π5′ sensitivities are affected by changes in π4 and π5 and also by some factor which manifests when π4 and π5, are altered. This factor is not related to the spectral sensitivities of the other mechanisms.