Much research has been done on using pre-notification letters or postcards to improve survey response among de novo contacts. Those gains are generally 4-6 percentage points in mail surveys and thus a recommended part of the tailored design method described by Dillman. The reasoning is thought to be that people prefer to know that they are to be part of something important and can look for it to occur soon in the mail. It is also possible that it contributes to the main mail survey envelope actually being opened. On the other hand, members of a pre - recruited Web panel expect to do surveys on some periodic basis on the Web. A part of the panel protocol is for notifications to occur via email. When a survey is ready, an email invitation is sent with an active link to the survey questionnaire embedded in the text. This is and has been standard procedure for virtually all extant Web panels, including the recently created probability-based American Trends Panel (ATP) operated by Abt SRBI for the Pew Research Center. The relatively new ATP had several surveys administered in 2014 using email notifications. Persistent non- responders, however, were still present. In the event that email invitations were possibly not being seen, an advance postcard was mailed to panelists as an experiment for one survey. Panel members with a mailing address were randomized into two groups. About half (n=2,080) were mailed the advance postcard announcing their upcoming survey plus sent their usual email invitation. The other half (n=2,063) were sent the email invitation only. The group receiving the postcard had a 5.3 percentage point higher participation rate for the Web survey (p<.001). A comparison of demographic characteristics plus survey findings for responders and non-responders is shown to demonstrate any observed bias between the two groups.