The mouth alcohol effect is a commonly raised defense in criminal courts with many studies having been conducted to quantify the phenomenon. This study examined the frequency of breath sampling and its potential significance in underestimating the duration and magnitude of the mouth alcohol effect in real life forensic situations. In addition, it examined the effectiveness of the Intoxilyzer 5000C mouth alcohol detection system. Three trials were conducted with 19 female and 11 male subjects who were alcohol-free, rinsed their mouths for 20 seconds with 20 milliliters of vodka diluted to 20 percent v/v alcohol, and then expectorated. The subjects provided breath samples into an Intoxilyzer 5000C, a Canadian approved breath alcohol testing instrument. Study results indicate that as the breath sampling frequency increased, the duration and magnitude of the mouth alcohol effect decreased, demonstrating that unrealistic experimental designs may limit the forensic applicability of conclusions in many mouth alcohol studies. In addition, the effectiveness of the mouth alcohol detector of the Intoxilyzer 5000C increased with increasing mouth alcohol concentration (MAC). It is recommended that forensic alcohol experts carefully evaluate the experimental conditions used in the mouth alcohol studies when applied to actual forensic situations. References