Chickens were treated prophylactically with the soluble products from Con A-stimulated T-lymphocytes from Salmonella enteritidis-infected chickens in order to investigate the effect of such prophylactic treatment on organ invasion by S. enteritidis. At 18 days of age, chicks were injected intraperitoneally with one of the following: A) the Amicon YM 10 ultrafiltrate from immunized chickens, B) the Amicon YM 10 ultraretentate material from immunized chickens, or C) the Amicon YM 10 ultraretentate material from control nonimmune chickens. Thirty minutes after lymphokine injection, all birds were challenged per os with 10(8) colony-forming units of S. enteritidis. At both 1 and 6 days post-challenge, prophylactic treatment of chickens with the immune retentate resulted in a 51-60% reduction in S. enteritidis organ invasion. The reduction in S. enteritidis organ invasion was associated with a significant increase in lamina propria thickness based on morphometric analysis (P < 0.05). These results demonstrate that the prophylactic administration of S. enteritidis-immune lymphokines induces protection against S. enteritidis organ invasion, which is associated with a measurable microanatomical change in the cecal mucosa.