Tubal pregnancy remains a clinical challenge in spite of improvements in diagnostic tests and procedures. In a prospective study we evaluated the role of the serum creatine kinase as a possible marker for tubal pregnancy. Three groups of 17 patients each were included in the study: group A, documented tubal pregnancy; group B, spontaneous abortion; and group C, normal pregnancy. Serum was tested for creatine kinase in all of the patients. Creatine kinase level was > 45 IU/L in all patients with tubal pregnancy, significantly higher than the level in patients in either of the two other groups (p < 0.0001). We conclude that a high serum creatine kinase level can be an important diagnostic test in the evaluation of a suspected tubal pregnancy.