Aha1 is a member of the Hsp90 cochaperone family, and is thought to stimulate Hsp90 ATPase activity bycompeting with p23 and other co-chaperones forHsp90 binding (1, 2). It may affect a step in theendoplasmic reticulum to Golgi trafficking. Aha1 alsointeracts with HSPCA/Hsp90 and with the cytoplasmictail of the vesicular stomatistis virus glycoproteins(VSV G) (3). Aha1 is expressed in numerous tissues,including the brain, heart, skeletal muscle, andkidney, and at low levels, the liver and placenta. Aha1might be a potential therapeutic strategy to increasesensitivity to HSP inhibitors (4).