Gilbert's syndrome is a frequent clinical condition with indirect hyperbilirubinemia, with controversial pathogenesis, nosography, and diagnostic criteria. Reliability of diagnostic test (caloric intake restriction and phenobarbital induction), as well as bilirubin modifications after physical exercise, were assessed in 7 patients with the disease. Phenobarbital induction appears to be the most suitable and reliable test for clinical non-invasive diagnosis of Gilbert's syndrome.