A 10-year-old 57-kg sexually intact female alpaca was presented because of a 3- to 4-month history of aggressive behavior (attacking and charging herdmates). The alpaca previously had several successful pregnancies, with her last cria born approximately 1.5 years earlier. There had been no other male exposure since that breeding, as the owners only have females and 1 gelding (housed separately). The referring veterinarian collected blood for hormone testing through the Cornell University Animal Health Diagnostic Center in Ithaca, NY. Serum progesterone concentration was 10.49 ng/mL, consistent with progesterone concentration reference limit of > 2 mg/mL during pregnancy in camelids.