Septicaemia still presents a major diagnostic and therapeutic challenge to the clinician. Most cases are hospital-acquiredand the reasons for their increasing prevalence are discussed, with reference to predisposing factors and opportunistic infections. The pathology and bacteriology of proven cases (positive blood cultures) in 1974 in a modern children's and maternity hospital complex are presented. Gram-positive and Gram-negative varieties are compared and the molecular biology and mechansims of endo- and exotoxaemia described. Successful therapy demands correct choice of antibiotic and the development of shock requires skilled supportive measures. For the former a rational scheme is outlined and a plea is made for collection of data for this purpose. Polypharmacy is deprecated and either an aminoglycoside or a cephalosporin forms the mainstay of therapy. The emergence of Bacteroids sp. in cases of abdominal and puerperal sepsis necessitates addition of a lincomycin or metronidazole. Superinfection with systemic candidiasis requires 5-fluorocytosine.