['Serum free fatty acid (FFA) composition and abnormal fatty acid metabolism have been implicated in the pathogenesis of nonalcoholic steatohepatitis (NASH). Therefore, we determined if the serum FFA composition can provide accurate diagnosis of NASH.', 'We compared fasting serum FFA compositions in 20 patients with simple steatosis to those in 77 patients with NASH, including 65 patients with early-stage NASH.', 'By univariate analysis, the proportions of serum free myristic acid (P\xa0=\xa00.002) and palmitoleic acid (P\xa0=\xa00.033) and the stearoyl CoA desaturase (SCD)-1 index (P\xa0=\xa00.047) were significantly elevated in NASH patients in comparison to patients with simple steatosis. Only the serum free myristic acid proportion was significantly elevated in the early-stage NASH group in comparison to the simple steatosis group (P\xa0=\xa00.003). Multiple logistic regression analysis demonstrated that the serum free myristic acid proportion was significantly elevated in all patients with NASH (P\xa0=\xa00.011) and the subset of patients with early-stage NASH (P\xa0=\xa00.012) in comparison to those with simple steatosis. The area under the curve (AUC) for the serum free myristic acid proportion was 0.734 to detect NASH and 0.719 to detect early-stage NASH in comparison to simple steatosis.'] Is plasma free myristic acid proportion a predictor of nonalcoholic steatohepatitis?