Riboflavin deficiency almost always occurs in connection with other vitamin deficiencies. The most common causes are alcoholism, interactions with a variety of medications, dietary inadequacy, and the other causes of protein-calorie undernutrition. Symptoms include anemia, corneal vascularization, weakness, seborrheic dermatitis, glossitis, angular stomatitis, and cheilosis. A riboflavin deficiency diagnosis can be confirmed by measurement of the riboflavin-dependent enzyme erythrocyte glutathione reductase. Readers should note that activity coefficients greater than 1.2-1.3 are suggestive of riboflavin deficiency. Patients can be treated by consuming the vitamin itself (5-515 mg/day) or foods such as fish or dairy products. While riboflavin can be provided parenterally, practitioners should note that the vitamin does not dissolve well in aqueous solutions.