The blood chemistry was studied in 140 spinal cord injury (SCI) patients (acute injury ward), including 18 patients who developed heterotopic ossification (HO). Comparisons between the HO and non-HO groups were made to determine if the alkaline phosphatase (AP), inorganic phosphorus (P), or calcium (Ca) levels were of diagnostic value. The results showed that AP, P, and Ca by themselves were of little help in the diagnosis of HO. However, the combination of elevated AP and P was significant, especially if both were consistently elevated. There were no significant differences between the HO and non-HO groups concerning completeness or level of spinal injury.