ABSTRACT.The spectral sensitivity and flicker fusion frequency (FFF) of wild‐type and salmonGlossina morsitans morsitansWestwood (Diptera, Glossinidae) were compared electroretinographically (ERG). Spectral sensitivity curves were similar in shape for dark‐adapted wild‐type and salmon flies, but salmon flies were over 100 times as sensitive as wild‐type flies over much of their sensitivity range. Estimation of the spectral absorption curve (from the differences in ERG sensitivities) for the pigment absent from (or present in low concentration in) the salmon eye suggests that the pigment is an ommochrome. FFF at threshold light intensities was similar in wild‐type and salmon flies, but at higher light intensity (1.3 °W/cm2) the FFF of salmon flies increasedc.200–300%, due to the capacity of the salmon eye to adapt rapidly to the flicker stimulus. Body weight had little effect upon spectral sensitivity and FFF. Wild‐type males were more sensitive to yellow‐green light and had higher FFF than did wild‐type females. Salmon males and females did not differ in spectral sensitivity, but females had higher FFF (when tested with 520‐nm light) than did males. Old wild‐type females did not differ from young females in either spectral sensitivity or FFF. However, old salmon females were more sensitive but had lower FFF than young salmon females. Food deprivation reduced spectral sensitivity and FFF in wild‐type males but not in salmon males. Irradiation (10.5 krad) reduced spectral sensitivity (c.75–375%) and FFF (c.30%) in wild‐type males. The greatly increased spectral sensitivity and FFF in salmon flies indicate that these flies may behave differently from wild‐type flies in the field. Differences in the way spectral sensitivity and flicker discrimination are affected by dark and light adaptation, and by such factors as age and sex, indicate that these measurements ar