The photoperiod (i.e., constant light vs a 14/10 hour light/dark cycle) and "physical" crowding (group caging) on Uinta ground squirrels (Spermophilus armatus) was investigated to ascertain what effects these two environmental parameters would have on testicular metabolism of serotonin (MA8 activity) and melatonin synthesis by pineal glands in organ culture. Testicular MAQ activity was decreased by both constant light and crowding.