Three antibiotic formulations, oxytetracycline (A) in propylene glycol and oxytetracycline (B) in polyvinyl pyrrolidine and pyrrolidino-methyltetracycline in an oil suspension were given to calves by the intramuscular route. Only oxytetracycline (A) appeared to cause much pain after injection.The half-time elimination (t((1/2)cl)) for oxytetracycline (A) was 14.000 +/- 3.580 h for oxytetracycline (B) 10.290 +/-5.159 h and for pyrrolidinomethyltetracycline 8.160 +/- 0.920 h. The rate of elimination ;beta slope" for oxytetracycline (A) was 0.052 +/- 0.012 h(-1) for oxytetracycline (B) 0.077 +/- 0.261 h(-1) and for pyrrolidinomethyltetracycline 0.086 +/- 0.010 h(-1). The Y intercept of the "beta" elimination slope C(os) (mug/mL) for oxytetracycline (A) was 2.490 +/- 1.040, for oxytetracycline (B) 3.463 +/- 1.874 and for pyrrolidinomethyltetracycline 2.852 +/- 1.360.Pyrrolidinomethyltetracycline appeared to have a two component elimination curve, however, only the "beta slope" was used for the calculations.