Having a reliable method of delivering cells to polymer scaffolds in vitro is fundamental to the development of tissue engineered structures. This paper compares the efficacy of two rotating systems for this purpose. Ten conduits, measuring 40 mm by 10 mm, were fabricated from polyglycolic acid mesh and poly-4-hydrobutyrate. Five conduits were placed in a rotating wall vessel (RWV, Synthecon Inc., Houston, TX), developed by the National Aeronautics and Space Administration (NASA); five conduits were also placed in rotating individual sealed tubes (RISTs). Medium in the RWV was left unchanged for the duration of the experiment; medium in the RISTs required daily change. Samples of the discarded medium and samples from the RWV were analyzed for pH, pCO2, pO2, and lactate concentration. Constructs were assayed for DNA content as a surrogate for cell number. In the RWV, pH, pCO2, and pO2 remained stable, while the lactate concentration gradually increased. The measure of pO2 did not differ significantly between the RWV and the RISTs, but the pH was lower and the pCO2 and the lactate concentration measurements were higher in the RIST system at each time point (p = 0.001). After 6 days (p = 0.001), the total DNA per conduit was 226 ± 7 μg for the conduits seeded in the RISTs and 396 ± 18 μg for the conduits in the RWV, suggesting that the RWV is superior to the RIST system for delivering cells to polymer scaffolds.