Various plant secondary products have been implicated in the promotion of good health or the prevention of disease in humans, but little is known about the way they are absorbed in the gut, or in which tissues they are deposited throughout the body. While these issues could be studied if the phytochemicals were isotopically labeled, generating labeled molecules often is problematic because many compounds of interest can be synthesized only in planta at present. In order to generate ¹⁴C-labeled phytochemicals of high radioactive enrichment, we developed an enclosed-chamber labeling system in which cell suspension cultures can be safely and efficiently grown when supplied with ¹⁴C-enriched precursors. The system is designed to hold culture flasks within a clear, polyacrylic compartment that is affixed to the top of a rotary shaker. The flow-through gas exchange nature of the system allows for O₂ replenishment and complete capture of respired ¹⁴CO₂ throughout the entire period of cell culture. Air is circulated internally with the aid of a small fan, and chamber air temperature is monitored continuously with an internal temperature probe and data logger. Production runs of 12–14 d with Vaccinium pahalae (ohelo berry) and Vitis vinifera (grape) suspension cultures, using [¹⁴C]sucrose as the carbon source, demonstrated a 20–23% efficiency of ¹⁴C incorporation into the flavonoid-rich fractions. Further studies with ohelo cell cultures showed that flavonoids were produced with either sucrose or glucose as the carbohydrate source, although flavonoid productivity (measured as anthocyanins) was higher with sucrose. This comprehensive chamber system should have broad applicability with numerous cell types and can be used to generate a wide array of labeled phytochemicals.