A haematological survey of farmed fallow deer (Dama dama) and red deer (Cervus elaphus) was carried out. In the winter period the red blood cell (RBC) count was 9.0 x 10(12)/L in adult fallow-does, and 6.1 x 10(12)/L in fawns. The haemoglobin (Hb) level and mean corpuscular volume (MCV) were also significantly (P < 0.05) lower in fawns than in adult fallow deer. In blood samples taken from red deer in different physiological and nutritional periods, the stags showed the lowest mean RBC count in January (4.7 x 10(12/L) and the hinds during lactation (6.3 x 10(12)/L). The mean RBC count of samples taken from a group of red deer fawns at five different times between 1 week and 1 year of age varied between 5.8 and 7.0 x 10(12)/L. In red deer herds the RBC count showed minor variations and the Hb concentration was almost constant in the different periods. The coefficient of correlation between RBC and Hb was 0.66 and 0.58 in fallow deer and red deer, respectively. Studying the blastogenic transformation of lymphocytes by immunological tests, a higher rate of response to non-specific mitogens (Phaseolus vulgaris, PHA; concanavalin A, Con A) was found in farmed deer (> 30%) than in deer captured in the wild and kept under farm conditions for 10 or 13 months (< 20%).