In the setting of ethylene glycol (EG) poisoning, a falsely elevated serum lactate concentration is suggested to be an assay cross-reaction with glycolate, but a concentration-dependent relationship has never been identified. We correlate serum lactate and glycolate concentrations in a case of severe EG poisoning. Serial EG [by gas chromatography (GC)], glycolate (derivatized to methyl glycolate, analysis by GC), and lactate (both enzymatic spectrophotometry and GC) concentrations were correlated at five time points. False-positive lactate was confirmed by absence of lactate on GC analysis. The correlation coefficient (Pearson's r) between lactate (by enzymatic spectrophotometry) and glycolate was 0.984 and was statistically significant (p < 0.01). The mean lactate/glycolate conversion factor was 2.58 +/- 0.95. We demonstrate the linear correlation between falsely elevated serum lactate and glycolate concentrations in a case of severe EG poisoning. Our data provide further support to the belief that the lactate assay may cross-react with glycolate in EG poisoning.