Haematological and clinical effects were evaluated after multiple blood samplings over 24 h in the laboratory rat and for up to 22 days after collection to determine the time required for a return to baseline values. Male and female Sprague-Dawley rats (n = 7/sex/group) were bled 4 times over 24 h and blood samples of 1.2, 1.6, 2.4 and 3.2 ml were taken. There were no adverse clinical signs and no statistically significant differences in body weight, body weight gain and food consumption. The acute effect on main haematological parameters of blood removal over 24 h consisted of reductions of red blood cell count, haemoglobin and haematocrit which were similar for blood removal exceeding 7.5% and less than 15% of circulating blood volume, and the reductions were positively related to the amount of blood loss beyond 15%. Time to recover to baseline values was also proportional to the initial blood collection volume and was estimated to range from 48 h for amounts from 5% to below 7.5%, 12 days for amounts from 7.5% to up to 20% and 19 days for amounts above 20%. Recommendations are made concerning suitable blood collection regimes.