Non-protein nitrogenous substances include urea, uric acid, creatinine, amino acids, ammonia, purines and pyrimidines. Urea is the end product of protein catabolism, and major nitrogenous waste excreted urine; uric acid is the end product of purine, and creatinine is derived by dehydration of creatine in muscle. Serum and urinary levels of are elevated in gout. Specific tests for urea, uric acid and creatinine are explained.