Oxytocin (OT) and its receptor (OT-R) are implicated in the etiology of autism spectrum disorders (ASD), and OT-R is a potential target for therapeutic intervention. Very few nonpeptide oxytocin agonists have currently been reported. Their molecular and in vivo pharmacology remain to be clarified, and none of them has been shown to be efficient in improving social interaction in animal models relevant to ASD. In an attempt to rationalize the design of centrally active nonpeptide full agonists, we studied in a systematic way the structural determinants of the affinity and efficacy of representative ligands of the V1a and V2 vasopressin receptor subtypes (V1a-R and V2-R) and of the oxytocin receptor. Our results confirm the subtlety of the structure-affinity and structure-efficacy relationships around vasopressin/oxytocin receptor ligands and lead however to the first nonpeptide OT receptor agonist active in a mouse model of ASD after peripheral ip administration.