By using parallel culture techniques 330 blood specimens steming from patients of an intensive care unit were cultured simultanously in 3 media containing 0.05% Na-Poly-anetholsulfonate. Otherwise having an identical composition the media differed in the following respects : the isotonic medium A and the - by additional content of 10% sucrose - hypertonic medium B were used for aerobic culture. The anaerobic and isotonic medium C contained 2% Proteose-peptone, additionally. Without regards to the isolation of strictly anaerobic bacteria a total of 114 positive bloodcultures was obtained (tab. 1). The use of medium A resulted in 81 positive bloodcultures, that of medium B and C in 93 and 50, respectively (tab. 2). With the combined use of media A + B 103 positive bloodcultures would have been detected, with B + C 102, but with A + C 92 only (tab. 2). Of all 3 media the hypertonic medium B promotes bacterial growth most efficiently, but 13 strains grown in A did not grow in B (tab. 3), a fact that leads to the conclusion that isotonic as well as hypertonic aerobic media are employed in parallel advantageously. The effect of the hypertonic medium was expressed most distinctly with the isolation of grampositive bacteria (tab. 4). As during the period of this investigation the intensive care unit was afflicted by an outbreak of Serratia marcescens the predominance of this species among the other isolated microbes (tab. 5) is not surprising. While no difference of detection-time was observed between A and B, microbial growth in medium C seemed to be slower (fig). It was concluded that the use of 3 media, aerobic isotonic and hypertonic as well as anaerobic isotonic should be employed whenever possible.