The prophylactic treatment of neonatal broiler chicks with lymphokines derived from S. enteritidis-immurazed chickens (SE-ILK) was evaluated for its effect on the birds' resistance to an experimental infection S. enterica ser. gallinarum (SG). On the day of hatch, chicks were injected intraperitoneally with either SE-ILK, control non-immune lymphokines (NILK), or were left untreated. Thirty minutes later, all chicks were orally gavaged with either 10(4) colony forming units (CFU) or 10(6) CFU SG. The chicks were observed twice daily for 10 days for morbidity and mortality. Chicks that died during the experiment had their livers cultured for SG. The survivors were killed and their livers, spleens and caecal tonsils cultured for SG. The prophylactic treatment of chickens with SE-ILK induced significant protection against extraintestinal SG infection when compared to the NILK-treated or non-treated controls as evidenced by: (1) a significant reduction (P< 0.005) in the mortality of chicks challenged with either 10(4) and 10(6) CFU SG; (2) an increased average weight gains of chicks challenged with either 10(4) and 10(6) CFU SG; and (3) a significant (P< 0.001) reduction in the number of chicks with organs culture-positive for SG. The results suggest that the prophylactic administration of SE-ILK can confer non-specific protection to chicks against a pathogenic species of Salmonella resulting in reduced morbidity, mortality, and organ infectivity caused by SG infections of broiler chicks, while enhancing performance during the first 10 days of Ufe.