In an attempt to identify the heterozygotes state for progressive intrahepatic cholestasis (PIC), hepatic excretory function (131I rose bengal half-life (t1/2) and bromosulpthalein-transport maximum (BSP-Tm) was studied in controls and in eight members of a family, two of whom are affected with PIC. Values for 131I rose bengal t1/2 varied over a wide range in normal controls and were normal in patients with the syndrome of cholestasis and peripheral pulmonic stenosis in whom BSP-Tm and 45 min % retention were abnormal. 131I rose bengal t1/2 was abnormal in seven of eight family members. Despite this, BSP studies, including Tm, percent retention at 45 min, clearance were normal in all unaffected family members with the exception of the mother who has a reduced BSP-Tm. Fasting serum bile acid studies were normal in all unaffected family members. These studies do not clearly define the inheritance in this syndrome and suggest that any of the following three possibilities exist: 1) that the methods employed were not sensitive enough to detect heterozygotes, 2) that the inheritance in this syndrome is heterogenous; for instance, compound heterozygotes or autosomal dominant, or 3) that the family studies here represents a syndrome different from PIC.