Five commonly practised veterinary procedures were studied: Palpation per rectum of the reproductive tract, intramuscular injection, single venepuncture, repeated venepuncture and jugular vein catheterisation. Plasma cortisol concentrations increased from baseline values of approximately 2 ng/ml to maximum mean values between 6.5 +/- 2.5 ng/ml and 13.8 +/- 5.6 ng/ml approximately 13 to 27 minutes after each manipulation. Baseline values occurred approximately 80 minutes later. In the control bleeding periods unacclimatised cows initially had high values of plasma cortisol (5 to 10 ng/ml) which returned to baseline after two hours, ie, before beginning any procedure. There were no statistically significant changes in luteinising hormone concentrations. The concentration of 13,14 dihydro, 15-keto prostaglandin F2 alpha (PGFM) increased from 61.0 +/- 4.6 pg/ml to 209.8 +/- 152.1 pg/ml in three out of five cows palpated on days 16 and 19 of the oestrous cycle. Increases did not occur in five other cows palpated during the follicular phase, nor in five cows palpated on day 12. However, after palpation on day 8, one animal did have concentrations of PGFM similar to those occurring during spontaneous release on days 18 to 20 of the oestrous cycle.