A batch of 95% ethanol caused unusually strong disordering of biomembranes, which could be detected either by fluorescence anisotropy in synaptosomal membranes or by electron paramagnetic resonance spectroscopy in erythrocyte membranes. The contaminated batches of ethanol were visibly fluorescent when evaporated on filter paper. The adulterants were separated by capillary gas chromatography and the ubiquitous pollutant dioctylphthalate was identified by its low resolution electron impact mass spectrum. The remaining peaks, which were not recognized by any of the available mass spectral libraries, were identified by high resolution electron impact and chemical ionization mass spectrometry and low resolution tandem mass spectrometry using fast atom bombardment ionization; they were triethylene glycol esters and aryl phosphates. All the contaminants are industrial plasticizers. Distillation resulted in loss of the strong disordering properties of the alcohol.