A widely used breath analysis instrument was adapted for the noninvasive determination of blood alcohol in small animals. The instrument's response to ethanol in vapor above the lacrimal fluid was analyzed subsequent to taking vapor samples from a small eye cup for 15 sec. After ethanol administration (1.5 g/kg, orally) to rats, eye vapor measurements and venous blood samples were obtained over 5 hr. Eye vapor measurements were transposed into blood alcohol concentrations and compared with concentrations obtained by gas chromatographic analysis of blood. The correlation of concentrations obtained by the two methods yielded correlation coefficients of 0.93 and 0.95 depending on the calculation used. Eye vapor response and blood alcohol concentration were also found to be highly correlated (r = 0.96) after alcohol administration to mice and sampling for 2.5 hr after ethanol administration. Kinetic profiles obtained by eye vapor analysis and gas chromatography are virtually identical. The method described allows widespread use of a new, noninvasive approach to alcohol analysis in laboratory animals.