691 patients with clinically and bacteriologically established sepsis were included in three prospective studies conducted at a university hospital with 1,300 beds in 1979, 1982 and 1986. Only 22.4% of the patients did not suffer from severe underlying diseases. There was a fairly even distribution of gram-positive and gram-negative organisms among the isolated pathogens. A marked increase was seen in the incidence of polymicrobic and mycotic infections. The most frequently isolated bacterial species were E. coli (24.9%), Staph. aureus (19.5%), Staph. epidermidis (8%), Enterococci (4.8%) and Klebsiellae (4.6%). 26.8% of the patients died. The mortality rate showed a marked decrease from 33.6% in 1979 to 22.4% in 1986.