The myc family of proto-oncogenes belongs to the basic helix-loop-helix leucine-zipper (bHLHZ) class of transcription factors. Myc proteins function as transcriptional activators through heterodimerization with Max, but might also act as negative regulators of transcription. Identification of genes directly controlled by Myc-Max has proved difficult, but recent work is producing a growing list of candidates. Results to date suggest that Myc-Max influences cell growth and proliferation through direct activation of genes involved in DNA synthesis, RNA metabolism and cell-cycle progression.