The apparent 'third quarter' phenomena in polar missions where low points in mood and morale are experienced just past mid-season were investigated. A prestudy assessment was conducted on the winter over personnel (from the 1995-1996 winter) at Scott Base to determine the appropriate content and methods of implementation. The phenomenon was then assessed by using well validated psychological scale ... surveys (personality measures, single day mood scale and single week mood scale). Measurements of mood for staff employed for the 1996-1997 winter (~13 months of work starting in October) were conducted a week prior to deployment to Scott Base (baseline), post deployment (one week after arrival), prior to the start of the winter season and prior to their return to New Zealand the following spring. Interviews were conducted throughout the season to gain reasons for the change in mood over the course of deployment. Opportunistic surveys were conducted on summer support personnel at the base for providing comparison with a short summer stay versus longer summer and winter stays. The results tested the assumption of the third-quarter phenomenon and examine alternative explanations for variations in mood.