All paediatric patients with the diagnosis of diphtheria who were seen at the Department of Child Health Ujung Pandang General Hospital from October 1987 to October 1989 were evaluated for bull-neck, ECG patterns and serum creatine phosphokinase (CPK) values. Their ages ranged from 1 year and 2 months to 13 years with a mean of 6.54 +/- 3.09 years. Males and females were affected in a ratio of 1:1. Of 39 patients included in the trial, 28 were classified as having normal ECG and 11 as having abnormal ECG on admission. During hospitalization, 56.4% of cases showed ECG changes. All patients had raised serum CPK levels on admission. This increase was 14.6 times the normal level in cases with abnormal ECG and only 3.0 times in those with normal ECG (p < 0.01). The highest levels of serum CPK were noted in the first week, then returned to normal in the second week and decreased further in the third week. It became also evident that patients who developed abnormal ECG later on, had already demonstrated an increased serum CPK level of 5.2 times the normal levels on admission. Bull-neck appeared in 19 out of the 39 patients. Patients with bull-neck differed very significantly (p < 0.001) from those without bull-neck in either the frequency of the occurrence of abnormal ECG patterns or the mean CPK serum levels.(ABSTRACT TRUNCATED AT 250 WORDS)