The present invention concerns combination of an amount of a GPR119 agonist with an amount of a dipeptidyl peptidase IV (DPP-IV) inhibitor such that the combination provides an effect in lowering a blood glucose level or in increasing a blood GLP-1 level in a subject over that provided by the amount of the GPR119 agonist or the amount of the DPP-IV inhibitor alone and the use of such a combination for treating or preventing diabetes and conditions related thereto or conditions ameliorated by increasing a blood GLP-1 level. The present invention also relates to the use of a G protein-coupled receptor to screen for GLP-1 secretagogues.