The objective of this study was to determine the effect of carprofen (C) administration before banding or burdizzo castration of bulls on cortisol, in vitro interferon-gamma (IFN-gamma) production, acute-phase proteins, feed intake, and growth. Fifty Holstein Friesian bulls (5.5 mo old; 191 +/- 3.7 kg) were blocked by weight and assigned randomly to 1 of 5 treatments (n = 10/treatment): 1) untreated control (2) banding castration at 0 min (Band); 3) Band following an i.v. injection of 1.4 mg/kg of BW of C at -20 min (Band+C); 4) Burdizzo castration at 0 min (Burd); or 5) Burd following 1.4 mg/kg of BW of C at -20 min (Burd+C). Castration acutely increased plasma cortisol concentrations compared with control; no significant differences occurred in peak and interval to peak cortisol responses between Band and Band+C or Burd and Burd+C groups. The administration of C in Band+C reduced (P < 0.05) the cortisol concentration between 6 and 12 h postcastration compared with Band animals. Overall, the integrated cortisol response was greater (P < 0.05) in the castrates than in control, whereas C treatments tended to reduce this response compared with Band (P = 0.08) and Burd (P = 0.07), respectively. Plasma fibrinogen was elevated in Band animals on d 14 and in Burd animals on d 3 and 14. Carprofen administration reduced Band- and Burd-induced fibrinogen production on d 14 and 3, respectively. Plasma haptoglobin was elevated in Band animals on d 3 and 35 compared with control, and C administration was effective in reducing the haptoglobin elevation on d 35 in Band+C compared with Band. There were no differences among treatments in in vitro IFN-gamma production induced by concanavalin A and phytohemagglutinin on d 1 and 2. Overall from d -1 to 16, there were no DMI differences among treatments. From d -1 to 35, there were no ADG differences among treatments. In conclusion, banding and burdizzo castration increased plasma cortisol with no change in in vitro IFN-gamma production. Carprofen (1.4 mg/kg of BW) tended to reduce the integrated cortisol response, and it reduced cortisol secretion in banded animals between 6 and 12 h postcastration. There was an increased acute-phase protein production following castration; this response was effectively moderated by the administration of C before castration.