After approval by the Ethics & Research committee of Hamadan University of Medical Sciences and obtaining written informed consent, 61 patients classified as ASA I (18–45 years) with gestational age 36-42 weeks who were scheduled for laboe under regional analgesia participated in this double blinded clinical trial. Patients were excluded for the following reasons: preeclampsia, chronic hypertension, diabetes,hepatic or renal disorders, allergy to drugs in the study, contraindication of neuraxial anesthesia,, mother addiction and drug abuse and any unexpected accident that need to cesarean section and privious history of pruritus or allergy to study drug . Before induction of spinal analgesia, baseline standard monitoring was recorded in a supine position by automatic monitoring (Novin S 1800, Saadat model). Spinal analgesia was administered by a 25 gauge Quincke needle (Mekon Medical devices Co. Shanghai China) at the L3-L4 inters pace, parallel to the dural fiber, while the patient was in the sitting position. Spinal analgesia consisted of 10 µg (2 ml) Sufentanil (Sufiject Aburaihan Co. Iran)administered in 12 sec. Patients were randomly allocated using opaque envelopes (block randomization with a block size of six) into three groups: groups1 and 2, in which the patients received 4mg ondansetron or 8 mg dexamethasone ,before induction of spinal analgesia, and group 0, in which the patients recieved normal salin as placebo. . To blinding the study, one anesthesiologist administered the spinal analgesia and randomized the patients, and another assistant performed drug preparation and injection. Systolic blood pressure (SBP), heart rate (HR), mean arterial blood pressure (MAP) and O2 saturation (SpO2) were recorded 1 min before (as baseline), and 5, 10, 15min after induction of analgesia, and there after in 15 minutes interval through the end of labor.scratching was observed and severity of pruritus was assessed by visual analogue scale of pruritus in above time intervals.