Serum uptake and excretion rates for some antibiotics are known for the bottlenose dolphin, Tursiops truncatus. We have, until now, inferred from this information for the proper therapeutic dose of the same antibiotics in larger species. In the investigative trials presented here, utilizing two Killer whales, Orcinus orca, one a female weighing approximately 10,000 pounds and the other a male weighing approximately 12,000 to 14,000 pounds, serum concentrations of orally administered Ampicillin at 5 mg/lb and Amoxicillin at 5 mg/lb were measured at 1, 2, 4, 8, 16, and 24 hours. Results show good absorption of both antibiotics with therapeutic levels remaining for up to 12 hours for Ampicillin and 24 hours for Amoxicillin at these dosages.