The occurrence and importance of secondary bacteremia in the pathogenesis of and response to therapy in meningitis is uncertain. Streptococcus pneumoniae type III was injected into the cerebrospinal fluid of the cisterna magna in anesthetized, curarized dogs, and sequential simultaneous samples were obtained from the superior sagittal sinus, cisterna magna, and peripheral blood. The results show that: (i) bacteria are rapidly transported from the cerebrospinal fluid to blood but only after active multiplication within the cerebrospinal fluid, and (ii) entrance into the blood from the cerebrospinal fluid occurs before the height of the febrile response or cerebrospinal fluid pleocytosis.