The physiological variations and the influence of sex and age on the serum biochemical profile of dogs were evaluated based on an analysis of 132 blood specimens from 44 newly weaned and young adult Doberman dogs, ranging in age from 2 to 36 months, from a private kennel. The analyses were processed colorimetrically in an automatic analyzer using commercial kits. The mean values of the serum biochemical parameters analyzed here remained mostly within the physiological reference intervals. The only differences were albumin, which showed higher values and chloride with lower values than those reported in the literature, suggesting that the animals were in good health. The age brackets showed significant differences in serum concentrations of total protein, albumin, globulins, albumin/globulins (A/G) ratio, urea, creatinine, cholesterol, total calcium, ionized calcium, phosphorus, iron, alanine aminotransferase (ALT) and alkaline phosphatase (ALP). In terms of sex-related differences, phosphorus was higher in males and the calcium/phosphorus (Ca/P) ratio was higher in females. Age appeared to influence several serum biochemical parameters in young Doberman dogs, especially up to 6 months of age, while sex influenced only the serum phosphorus concentration and the Ca/P ratio. [ABSTRACT FROM AUTHOR]