Creatine kinase isoenzyme analysis was performed on the cord blood of 125 infants who had undergone at least 30 minutes of intrapartum electronic fetal monitoring. The tracings were scored blindly according to severity of abnormal patterns, and the infants were grouped into ominous, intermediate, and normal scores. No differences were seen in creatine kinase MM or creatine kinase MB levels among the three groups. However, infants with ominous fetal heart rate patterns had higher creatine kinase BB levels and poorer outcome than infants with normal patterns.