Multiuser dynamic orthogonal frequency division multiple access (OFDMA) can achieve high downlink capacities in future wireless networks by optimizing the subcarrier allocation for each user.When it comes to the integration into current wireless local area network (WLAN) standards, dynamic OFDMA raises several implementation issueswhich are neglected in theoretical papers. Putting this emerging approach into practice requires to treat these issues accordingly and to demonstrate the feasibility of the system design. In this paper, we propose a dynamic OFDMA integration for the physical layer of the widespread IEEE 802.11a standard. To test our implementation and demonstrate its practical relevance we use a pragmatic approach: We prototype multiuser dynamic OFDMA on a real-time software-defined radio testbed for WLANs. We discuss details of our implementation and provide measurements showing that it does not introduce significant overhead into the IEEE 802.11a system at high subcarrier allocation quality. We particularly focus on the problems of our integration as well as the concepts and limitations of the used testbed.