1) A disease in which the metabolic products of phenylalanine and tyrosine accumulate, resulting in the deposition of homogentisic acid (a brown-black pigment) in the connective tissue. It occurs in alkaptonuria, but has also been observed in connection with exposure to certain chemicals (e.g., phenol, trinitrophenol, benzene derivatives).

2) A condition often associated with alkaptonuria and marked by pigment deposits in cartilages, ligaments, and tendons.