Abstract The Indian palm squirrel, Funambulus pennanti showed a seasonal testicular cycle characterized by a short period of sexual quiescence with arrest of spermatogenesis in November when daylength and temperature were decreasing. The period of sexual recrudescence started from December when daylength and temperature were minimal and humidity was changing. The testes remained sexually active during rest of the annum. The accessory sex organs as judged by their weight and fructose level in seminal vesicle, acid phosphatase activity in prostate gland and glycerylphosphoryl choline in epididymis followed the pattern of testes. An inverse relationship between the pineal and testes weight was observed. The pinealectomized squirrels (after 60 days) presented an active testes throughout the year. It may be suggested that in the absence of the pineal the squirrels were unable to respond to environmental cues, and thus maintained themselves sexually active. Due to differential threshold level of testosterone for the accessory sex organs, pinealectomy had no effect on the prostate gland and seminal vesicle while epididymal weight and its glycerylphosphoryl choline content were higher in pinealectomized animals. The above results indicate that the pineal gland of this tropical rodent mediates the environmental information for the regulation of its annual testicular cyclicity.