Semipreparative liquid chromatographic separation and subsequent off-line mass spectrometry have revealed caprolactam as a new contaminant in intravenous solutions. The content of the lactam was found to be 1.2-15.0 mg l-1 determined by liquid chromatography. Contamination is attributed to migration of caprolactam from the protecting plastic envelope through the PVC barrier and into the intravenous solution. Migration occurs during the final heat sterilization process.