The present investigation was undertaken to improve dosage regimens--using amoxycillin, chloramphenicol or trimethoprim/sulphadiazin--in Salmonella dublin or Salmonella typhimurium infected vealcalves. The pharmacokinetic of these drugs was studied after i/v, oral, and i/m administration (bio-availability, local irritation at the injection site, volume of distribution, and elimination half-life). The most important conclusion was that amoxycillin, chloramphenicol, and trimethoprim were suitable for oral administration to vealcalves, although the bioavailability of chloramphenicol and trimethoprim was significantly less when administered with a milk replacer concurrently. In vitro the antibacterial activities of these drugs were compared with each other. Addition of sulphadiazin to trimethoprim lowered its MIC for S. dublin, but it reduced the killing rate compared to that of trimethoprim alone. In the efficacy studies the activities of several serum enzymes and the plasma concentrations of Fe, Zn, Cu, and bilirubine were measured. Using optimal dose regimens based on MIC values and blood levels treatment with either of the three drugs was of equal efficacy.