The onium compound 2-(4-chlorophenylthio)-triethylamine (CPTA) was used to increase lycopene formation to levels approximating those in field-or glasshouse-grown fruit, and then growth regulators, sucrose and temperature were used to regulate lycopene accumulation. It was found that the native auxin indole-3-acetic acid (IAA) was substantially more effective than 2,4-dichlorophenoxyacetic acid (2,4-D) in promoting lycopene formation, sucrose inhibited lycopene formation (cell basis), and temperature produced a pattern similar to that observed in the field with a temperature optimum between 18 and 26 degrees C. Suggestions for further improvements in technique are included.