In wireless body area network (BAN) applications such as wearable computing, healthcare and sports, Bluetooth Low Energy (BLE) is a new and promising technology, which uses the unlicensed 2.4-GHz spectrum band for data transmission. Since there exist many wireless technologies operating in this frequency band, the issues of cross-technology interference and coexistence present a major challenge. In this work, we develop a testbed to conduct our experimental studies, focusing on BLE and its coexistence capabilities when being deployed in a dense environment, under possible interference from WiFi and ZigBee/IEEE 802.15.4. One scenario of interest is a network of several co-located BLE-based BANs, each of which is designed in a star topology with one gateway and multiple BLE sensor nodes. The second scenario represents a highly heterogeneous network where each BAN now carries both BLE and ZigBee sensors, while being exposed to interference from external WiFi transmission. Our results show that the performance of BLE is relatively robust to interference from other BLE transmission as well as those from nearby ZigBee and WiFi devices.