We recently experienced 4 cases of patients with falsely low total CK level, even though their actual levels were very high. At first tests, 3 of them revealed lower than 10 U/L with a warning sign of abnormal linearity from autoanalyzer and one of them showed the level within reference range (70 U/L; reference ranges, 55-215 U/L) without any warning sign. We used Hitachi 747 automatic analyzer for the evaluation. We got proper results when we diluted five to twenty fold the samples and tested them again. One of them was diluted 5 fold, one 10 fold, and two 20 fold and the results after dilution were from 12,876 to 39,780 U/L. Early consumption of the substrate seems to be the reason of falsely low level. LD activity of the same samples showed higher than reference range in all cases. We recommend the total CK level of the specimen to be rechecked when total CK is very low and the results of other related markers show high level.