To determine whether opiate consumption is affected by laboratory housing, individually caged and colony rats were given a choice between water and progressively more palatable morphine-sucrose solutions. The isolated rats drank significantly more of the opiate solution, and females drank significantly more than males. In the experimental phase during which morphine-sucrose solution consumption was greatest, the isolated females drank five times as much, and the isolated males sixteen times as much morphine (mg/kg) as the colony females and males respectively.