Although taurine is not dietarily essential for dogs, taurine deficiency and dilated cardiomyopathy (DCM) are sporadically reported in large-breed dogs. Taurine status and husbandry were examined in 216 privately owned Newfoundlands, a giant dog breed with high incidence of idiopathic DCM (1.3-2.5%). Plasma taurine concentration was positively correlated (P < 0.01) with plasma cyst(e)ine (r = 0.37) and methionine (r = 0.35) concentrations and was similar across age, sex, neutering status, body weight, and body-condition scores. Plasma taurine concentration was low (≤40 μmol/L) in 8% of dogs. Dogs with low plasma taurine were older, less active, had more medical problems and treatments, and had lower plasma albumin, cyst(e)ine, tryptophan, and α-amino-n-butyric acid concentrations than the other dogs (P < 0.05). Of 9 taurine-deficient, clinically evaluated dogs, 3 had DCM that was reversed by taurine supplementation and 1 had retinal degeneration. When given a diet apparently adequate in sulfur amino acids (5.4 g/kg) for 3 wk, 6 Newfoundlands (52.5 ± 2.3 kg, 3.5-7 y), compared with 6 Beagles (13.2 ± 2.3 kg, 5.5 y), had lower (P < 0.01) concentrations of plasma taurine (49 ± 16 vs. 97 ± 25 μmol/L) and cyst(e)ine and blood glutathione, lower (P < 0.01) de novo taurine synthesis (59 ± 15 vs. 124 ± 27 mg·kg-0.75·d-1), and greater (P < 0.05) fecal bile acid excretion (1.7 ± 0.2 vs. 1.4 ± 0.2 μmol/g). Newfoundlands would appear to have a higher dietary sulfur amino acid requirement than Beagles, a model breed used in nutrient requirement determinations.