A primary focus of signal transduction in B cells, from the pre-B cell to the mature B cell, is the B cell receptor complex. Here we describe work demonstrating the importance of signaling via the pre-B cell receptor complex (pre-BCR) to the pre-B cell transition, the central checkpoint in B-cell development. We have shown tht pre-BCR complex components Igalpha and Igbeta are critical to allowing the pre-B cell to move through this transition, but may not be required for allelic exclusion. Pre-BCR expression also directly affects the response of leukemic cells to steroid treatment, suggesting that signals initiated by the pre-BCR complex may present therapeutic targets in acute leukemia. Additionally, interleukin-7 may also modulate the response of leukemic cells arising from early B-cell stages to treatment. This observation has lead directly to proposals to test drugs which may antagonize early B-cell growth signals, such as rapamycin, in acute lymphoid leukemia.