By means of the diffusion test, the range of action of the ampicillin successive preparation spectacillin was determined using 12 000 pathological germs freshly isolated from in-patients. The result was a range of action similar to that of ampicillin. A comparison, however, is only possible in case the test platelets (without over-dosage) are each charged with exactly, e.g., 25 gamma. The analyses of serum concentrations have shown that spectacillin is satisfactorily absorbed after oral as well as after parenteral application. Thus, the calculation of the accumulated area of infinity beneath the serum concentration curve had the following results: After single intravenous injection of 1 g spectacillin (n equals 12) 51.46 gamma/ml - h; after single intravenous injection of 2 g spectacillin 86.20 gamma/ml - h; after intramuscular injection (twice) - interval of 12 hours - 29.94 gamma/ml - h after 12 hours; same values as before, but after 24 hours, 29.37 gamma/ml - h. After a single oral application of one capsule of spectacillin (capsule equals 500 mg), the value of the accumulated area was 8.46 gamma/ml - h. In analogy of the good absorption, excretion in urine/24 hrs (after application of 1 g spectacillin intravenously) was 61.74 p.c., after 2 g i.v. 54.30 p.c., and after applying twice 1 g spectacillin intramuscularly 61.40 p.c.; after oral application of 500 mg, the percentage was 28.42. Tolerance of spectacillin was good after oral as well as after parenteral application. No side effects were observed.