Chlorophyll a and b contents were determined in developing tomato fruit (Lycopersicon esculentum Mill. `Heinz 1350') at 5-day increments from 10 or 15 days past anthesis to fulIy ripe (55 to 60 days). When presented on a whole-fruit basis, chlorophyll a and b contents increased from 15 days past anthesis to 35 days and then decreased to zero at 55 days. Porphobilinogen (EC 188.8.131.52; PBG) deaminase activity was measured in extracts from the fruit, and changes in PBG deaminase activity correlated with changes in chlorophyll and protein contents with respect to fruit age. Partial characterization of tomato PBG deaminase enzyme showed similarities to PBG deaminase enzymes isolated from other sources.