Foveal increment threshold curves for two tritan obscrcers are reported. One of the tritans is a dichromat; the other is genetically a tritanope but has anomalous trichromatic color vision. The hypothesis was proposed that the complete tritanope would not demonstrate any of the three "blue" mechanisms (π1, π2, π3) but that for the incomplete tritanope one or more of these mechanisms would be evident. No curve inflection which could be attributed to a "blue" mechanism was elicited for either tritan, indicating that these mechanisms are absent or have severely depressed sensitivity. The tritan's "green" π4 mechanism has normal sensitivity at 580 nm and 480 nm but seems to have greater than normal sensitivity at 445 nm.