In Canada, a common defense to charges of driving under the influence of alcohol is known as the “Carter Defense” and involves blood samples with continuity problems. The goal of the current study was to evaluate the reliability of self-reported drinking defense scenarios compared to Intoxilyzer 5000C results. Self-reported drinking scenarios were examined and compared to Intoxilyzer 5000C results for 230 drivers charged with driving under the influence of alcohol in Ontario from 2000 through 2002. Standard forensic calculations were used to estimate blood alcohol concentrations (eBAC) from the drinking scenarios. These estimates were then compared to the lowest or first Intoxilyzer 5000C results. Results indicated that in 84 percent of the scenarios, eBAC's were over 10 milligrams of alcohol in 100 millilitres of blood lower than the Intoxilyzer 5000C results when using a rate of elimination of alcohol from the blood of 10 mg/100mL/h. In another 14 percent of the scenarios, eBAC's were within 10 milligrams of alcohol in 100 millilitres of blood of the Intoxilyzer 5000C results. When a rate of elimination of 20 mg/100mL/h was used, the number of eBAC's more than 10 milligrams of alcohol in 100 millilitres of blood increased to 96 percent of the drinking scenarios. Thus, the findings suggest that the majority of drinking scenarios provided as a defense against charges of driving under the influence are unreliable in comparison to the Intoxilyzer 5000C. Table, figures, references