Blood samples were collected from the bill sinus of nine free-living platypuses (Ornithorhynchus anatinus) within 12 min of capture of each and again after 1 to 12 hr, New South Wales, Australia, 1981 to 1988. In seven animals which were not anesthetized, there was a significant (P < 0.01) fall in lymphocyte count between the two samples. The reduction ranged from 10 to 58% of the initial lymphocyte count and caused a significant reduction in the total white cell count (P < 0.05). Both the neutrophil and the lymphocyte counts increased in two platypuses which were anesthetized with ether prior to collection of the second blood sample. We propose that the peripheral blood lymphocyte count is a simple means of monitoring the stress response of non-anesthetized, newly-captured platypuses and may be a useful adjunct to behavioral observation.