AbstractThe effects of blinding on cellular structure and porphyrin pigment content were studied in Harderian glands of pinealectomized and non‐pinealectomized adult female golden hamsters. Uterine weights were used as a criterion for pineal activity. Five weeks post‐operatively, no significant changes were observed in the Harderian glands or in the uterine weights of animals in either group. Eleven weeks post‐operatively, the blinded hamsters with intact pineal glands had significantly lowered uterine weights and Harderian glands that exhibited diminished amounts of porphyrin pigments and cellular characteristics of the male hamster. Harderian glands and reproductive organs from the 11‐week blinded‐pinealectomized hamsters did not differ from those of untreated