Serum myoglobin was measured in 40 children (mean age 5 yrs) following suxamethonium administration during anaesthesia for tonsillectomy. Half were given an i.v. induction while half were given an inhalation induction. Pre-treatment with alcuronium 0.04 mg kg-1 prior to suxamethonium administration was given to half the patients in each group. Mean pre-induction serum myoglobin was 11.8 micrograms litre-1. Following i.v. induction there was a marked rise of serum myoglobin in the control subgroup to a mean of 113 micrograms litre-1 20 min after suxamethonium administration. There was no such rise in the pre-treatment subgroup. In the inhalation control subgroup, there was a much larger mean rise to 537 micrograms litre-1 (significantly greater than in the control IV group), one patient reaching 2800 micrograms litre-1 20 min after suxamethonium administration. Pre-treatment greatly reduced but did not totally prevent the rise following inhalation induction.