OBJECTIVE: Bacteraemia concomitant with meningitis has been shown to greatly affect outcome. Consequently, the efficacy of serotype-specific anti-pneumococcal antiserum (APAS) was investigated in a rat model of pneumococcal meningitis. METHODS: Rats were infected with Streptococcus pneumoniae serotype 3. All rats received ceftriaxone starting 26 h post-infection. APAS was administered either at the time of infection or 26 h post-infection and effects were compared with rats treated with antibiotics only. RESULTS AND CONCLUSION: A significant clinical benefit was found when APAS was given at the time of infection whereas no effect was found when administered 26 h after infection. This work indicates that the clinical value of using APAS in pneumococcal meningitis may be limited