In this prospective blinded randomised study, 28 male 9 week old pigs of bodyweight 25 kg, were anaesthetised for castration using 5 mg/kg azaperone, 0.2 mg/kg butorphanol and 0.4 mg/kg meloxicam, in conjunction with either 15 mg/kg racemic ketamine (Keta-Race) or 9 mg/kg S-ketamine (S-Keta), all drugs being injected intramuscularly. Anaesthesia induction, maintenance and recovery were timed and scored. Insufficient anaesthesia was supplemented with ¼ the initial dose of ketamine or S-ketamine, respectively, administered intravenously. A t-test was utilised for analysis of timings, and, for repeated recovery time data, ANOVA was used. In relation to quantification and timing of supplemental drug doses, a chi square test was used and the scoring was analysed by two sample Wilcoxon rank-sum test. Ketamine re-dosing was required in 23 animals on a total of 46 occasions distributed evenly throughout both groups. The only group differences occurred during recovery, with the S-Keta group showing earlier movements, sternal recumbency and ability to stand. Three pigs in each group showed muscle fasciculations during the recovery period, while an additional two animals of the Keta-Race group exhibited marked and unacceptable paddling in recovery. In conclusion, S-ketamine at a dose rate of 60 % of that of racemic ketamine induced comparable anaesthesia for castration in pigs, but with superior recovery characteristics.