Alkaptonuria is a rare autosomal recessive disorder in which homogentisic acid accumulates and destroys connective tissue and bone, creating a condition called ochronosis. Symptoms generally begin in the third or fourth decade and progress to incapacitating spondylosis, arthropathy, and fractures by the sixth to eighth decades. Cardiac valve deterioration and renal and prostrate calculi also occur. Diagnosis is made by measurement of gram quantities of urinary homogentisic acid, which turns black on alkali treatment or exposure to oxygen. In the body, homogentisic acid forms a characteristic blue color in the cartilage of the ear and brown color in the sclera of the eye. The gene for homogentisic acid oxidase was isolated in 1996, and scores of different mutations have been defined. Only symptomatic treatment is available. We propose to investigate up to 200 alkaptonuric patients, particularly adults, during 5-day admissions, to define the disorder using current medical techniques. We will use our expertise in this disease to advise the population in terms of prognosis and therapy. Mutation analysis with correlation of genotype and phenotype, will be performed as a secondary goal. Finally, we will use this protocol to recruit patients into protocol 05-HG-0076. "Long-term Clinical Trial of Nitisinone in Alkaptonuria." Nitisinone is a very promising drug which inhibits the formation of homogentisic acid. The present protocol does not include treatment with nitisinone. Instead, we will examine patients, measure baseline excretion of homogentisic acid on repeated 24-hour urines, and characterize the signs and symptoms of alkaptonuria at different ages. This protocol will also serve as the "mother" protocol from which other alkaptonuria studies emanate.