Calcium (Ca), phosphorus (P), and magnesium (Mg) are important elements for body homeostasis in several diseases associated with imbalances in the plasma concentration of these ions. This is the first published report of reference intervals for Mg in association with Ca and P levels for psittacine species. One milliliter of blood was collected from 26 Hispaniolan parrots (Amazona ventralis) and 24 African grey parrots (Psittacus erithacus). The plasma concentrations of Ca, P, and Mg were determined for each sample. Statistical analyses were performed including all data (analysis 1) and after exclusion of the subjects with Ca ≥ 14.00 mg/dl (3.5 mmol) (analysis 2). The data from analysis 1 have a narrower interval than that observed in analysis 2. Following the normality test (Shapiro-Wilk, α  =  0.05), the univariate and mean procedures were run. For the reference intervals, the lower and upper values were used, after elimination of the outliers calculated by Blom scores from the ranked variables. The analysis 1 references for the Hispaniolans were Ca  =  8.80–10.40 mg/dl (2.20–2.60 mmol/L), P  =  1.80–4.40 mg/dl (0.58–1.42 mmol/L), Mg  =  1.80–3.10 mg/dl (0.74–1.27 mmol/L), and Ca∶P ratio  =  2.62–5.39; for the African greys analysis 1 references were Ca  =  8.20–20.20 mg/dl (2.05–5.05 mmol/L), P  =  2.50–5.90 mg/dl (0.81–1.91 mmol/L), Mg  =  2.10–3.40 mg/dl (0.82–1.4 mmol/L), and Ca∶P ratio  =  1.81–3.77. The analysis 2 references for the Hispaniolans were Ca  =  8.80–10.30 mg/dl (2.20–2.58 mmol/L), P  =  1.80–3.80 mg/dl (0.58–1.23 mmol/L), Mg  =  1.90–3.00 mg/dl (0.82–1.07 mmol/L), Ca∶P ratio  =  2.62–5.39; for the African greys analysis 2 references were Ca  =  8.10–10.80 mg/dl (2.03–2.7 mmol/L), P  =  2.40–5.30 mg/dl (0.78–1.71 mmol/L), Mg  =  2.00–2.60 mg/dl (0.82–1.07 mmol/L), Ca∶P ratio  =  1.67–3.50. The results of this study are important for evaluating Mg concentrations in relation to the Ca and P parameters in psittacines. This information will be particularly helpful for veterinarians evaluating the hypocalcemic syndrome in African grey parrots and other disease processes associated with Ca, P, and Mg physiologic imbalances.