The objective of this study was to measure parathyroid hormone (PTH), ionized calcium, and 25-hydroxyvitamin D concentrations in healthy intact adult ferrets. Serum was collected from 16 clinically healthy adult ferrets (8 males and 8 females). Concentrations of PTH and 25-hydroxyvitamin D were measured via commercially available radioimmunoassays validated for humans, dogs, and cats (PTH) plus horses (25-hydroxyvitamin D). Concentrations of ionized calcium (at pH 7.4) were measured using an ion-specific electrode. Median (minimum, maximum) concentrations were as follows: PTH 8.7 (2.2, 24.4) pmol/L, ionized calcium 1.15 (1.09, 1.25) mmol/L, and 25-hydroxyvitamin D 94 (61, 138) nmol/L). Female ferrets had significantly higher concentrations of PTH than male ferrets (female median: 17.1 pmol/L; male median: 6.9 pmol/L). Associations among PTH, ionized calcium, 25-hydroxyvitamin D, calcium, phosphorus, magnesium, and weight were evaluated. There was a weak negative correlation between PTH concentration and total calcium concentration in female ferrets. As none of these assays have been validated for use in ferrets, results may provide a baseline for clinicians evaluating ferrets for disorders of calcium homeostasis, parathyroid glands, and paraneoplastic syndromes.