Purpose: This study tested the clinical utility and relevance of serum phosphorus and magnesium as markers possibly useful to monitor training in athletes.Methods: Phosphorus and magnesium serum concentrations of 130 elite track and field athletes (65 males and 65 females, age range 20-30 years) from the National Athletics Sports Medicine Center database in Thessaloniki, Greece were measured. Results:Abnormal results were found in 61 (47%) athletes (32 men and 29 women). In male athletes, serum phosphate was higher than normal in 18% and decreased in 1.5%, whereas serum magnesium concentration was higher in 26%, and lower in 3%. Regarding female athletes, higher serum phosphate and magnesium levels were detected in 26% and 17% respectively, whereas decreased serum magnesium was found in 3%. The most common alterations were higher serum phosphate (29/61, 47%) and magnesium concentrations (28/61, 46%). Abnormalities of serum phosphorus and magnesium concentrations were detected in almost half of the athletes. Hyperphosphataemia and hypermagnesaemia were the most common abnormalities. Conclusion:The reference intervals used for general population cannot be used for athletes. Given the lack of pathological manifestations, the physiopathological significance of these findings is uncertain. Further studies on the interpretation of reported ion concentrations in athletes should take in account the type of sport practiced and also the possible variations during the training and competition season.