This paper investigates the return-path performance of a DOCSIS system (Cisco uBR7223) over an experimental two-way cable testbed. The packet error rate (PER), as well as the downstream and upstream TCP throughputs are studied as a function of upstream noise levels. For our DOCSIS upstream burst profile, the Carrier-to-Noise Ratio (CNR) threshold for one percent packet loss was found to be 11.5dB. The corresponding TCP throughputs for a cable modem with an upstream bandwidth of 1.6MHz were 4 Mbps downstream and 1Mbps upstream, respectively. We also evaluated the effectiveness of the forward-error correction code (Reed-Solomon) in recovering corrupted bits. With the maximum value of T (T=lO), the upstream CNR requirement improved by 3 to 4dB.