After the rapid and widespread emergence of online access panels, we are currently witnessing a new trend towards online custom panels that are specifically built, used and managed for research purposes of one company or its brand(s). This study compares the online access panel ‘XL Online Panels’ with a dedicated and branded online research panel from Heinz, generating conclusions on the relative advantages and disadvantages related to using either of them. Specific attention is paid to panel member conditioning (broadly defined as changes in response patterns over time due to learning) and quality. Differences in conditioning and quality in the Heinz and control panel are highlighted and the implications for online market research and panel management are discussed.