A chronic ethanol-fed rat model was used to determine the effect of alcohol ingestion on production of antibody to type 3 pneumococcal capsular polysaccharide. Sprague-Dawley rats were fed a liquid diet containing 36% of calories as ethanol (ethanol-fed), an isocaloric diet containing dextrin-maltose (pair-fed) or standard rat chow (chow-fed). After 7 days of feeding, the rats were vaccinated subcutaneously with placebo or with either 25 microg of type 3 pneumococcal capsular polysaccharide (SpnCP) or 5 microg of SpnCP linked to the protein carrier CRM197 (SpnCP/CRM197). Rats given the conjugated vaccine received a booster injection 14 days later. Maximum antibody titers were observed six days postvaccination for rats given SpnCP alone and 21 days postvaccination for rats given SpnCP/CRM197. All rats were infected transtracheally with 2-3 times the expected lethal dose50 for each feeding group of type 3 Streptococcus pneumoniae on the day of peak antibody titers. Mortality was recorded for a 10-day period. Vaccination with SpnCP increased survival of ethanol- and chow-fed, but not pair-fed rats. This protection was only statistically significant in the chow-fed group (p < 0.01). Vaccination with SpnCP/CRM197 moderately increased survival of rats in all three feeding groups, but this was not statistically significant in any of them.