Does it pay to pay online panel members? Two longitudinal experiments were conducted with an online panel to examine whether per-person payments via the online intermediary PayPal influence response and retention rates. Experiment 1 was a two-wave study. In the incentive condition, participants were promised 2 EUR to be paid upon completion of both waves, whereas control participants were not offered any incentive. For Wave 1, the promise of a payment had a negative effect on response, but a positive effect on retention. There was no direct effect on response and retention at Wave 2. Experiment 2 was a three-wave study. In the incentive condition, participants were promised 1.50 EUR for their participation at each wave, whereas in the control condition, participants were not offered any incentive. The promise of a payment had a negative effect on response in Wave 1, but a positive one on response in Wave 2. The payment had no significant effect on retention. In both experiments, retention at a given wave was found to be an indicator for response at the next wave, in that participants who dropped out at a given wave were less likely to respond at the next wave.