Abstract: A recombinant cell comprising a host cell containing a recombinant DNA sequence is disclosed. The recombinant DNA sequence comprises vector DNA and DNA which encodes a mammalian adrenergic receptor. The host cell is one capable of undergoing proliferation in response to activation of the adrenergic receptor. In one specific embodiment of the foregoing, the adrenergic receptor includes a mutation in the third cytoplasmic loop thereof which renders the adrenergic receptor constitutively active, and the host cell undergoes proliferation in response to the constitutively active adrenergic receptor. Also disclosed are in vitro assays employing the foregoing which are useful for screening test compounds for antitumor and antiatherogenic activity, along with a diagnostic assay for detecting the oncogenic activation of cells in a patient.