The neurotransmitter serotonin/5-hydroxytryptamine (5-HT) regulates a wide variety of neurological functions. A family of 13 receptors (12 GPCRs and one ion channel) mediate the effects of serotonin. The serotonin receptor 5-HT₇ is a Gs coupled receptor expressed in the brain (hypothalamus, hippocampus and frontal cortex) and in smooth muscle and GI tract. Systemic delivery of serotonin results in hypothermia, and pharmacological and genetic studies indicate that 5-HT₇ mediates this effect (Hedlund et al., 2003). In addition, 5-HT₇ appears to modulate circadian rhythms and smooth muscle relaxation, and is implicated as a target for sleep, particularly as related to depression, and migraine (Terron and Falcon-Neri, 1999; Mullins et al., 1999). Millipore's 5-HT₇ membrane preparations are crude membrane preparations made from our proprietary stable recombinant cell lines to ensure high-level of GPCR surface expression; thus, they are ideal HTS tools for screening of agonists and antagonists of 5-HT₇. The membrane preparations exhibit a Kd of 37.7 nM for [³H]-5-Carboxamidotryptamine (5-CT). With 30 nM [³H]-5-CT, 10 μg/well 5-HT₇ Membrane Prep typically yields greater than 4-fold signal-to-background ratio.