One of the most important challenges in medicine is decreasing the labor pain . Many different methods have been used including applying Transcutaneous Nerve Stimulation ( TENS) and inhalation of Entonox during labor. However the results are inconsistent. General objective of this study is determining the efficacy of TENS & ENTONOX in decreasing the labor pain. Specific objectives include comparison of the duration of first stage of labor in 3 groups, determining the trend of pain appearing in different dilatations in 3 groups, comparison of pain intensities in different dilatations in 3 groups, comparison of the amount of analgesics used, nausea & vomiting and apgar of newborn in 3 groups. Inclusion criteria are : Normal monofetus term pregnancy ( 37-42 weeks) , Normal vaginal delivery , lack of request for epidoral anesthesia , head down position of the fetus , uncomplicated pregnancy , less than 4 cm cervix dilatation , age of mother between 20-40 years & satisfying of mother regarding awareness of the methods used in the study. Exclusion criteria: Multifetus pregnancy, Hx of D.M, Hypertension, dermal skin infections, cardiovascular diseases, pacemaker , coagulation disorders or other diseases of the mother and preterm delivery. Sampling will be done by simple accessibility & the patients will be divided in 3 groups of TENS , Entonox and mixed group by random. Total numbers of patients are 117 with 39 patients in each group. Type of study is clinical trial. Analysis of the quality data will be done by descriptive statistical methods of X2 and of the quantity ones by ANOVA methods. Study will performed in Emamreza & Motazedi hospitals by gynecologic residents who assist in performing the medical examination and obtaining written consent from the patients. Our intervention will be done just in the first stage of delivery (dilatation of cervix 4-10 cm). VAS will be used for evaluation of pain intensity in the form of 10 cm ruler. Methodolgy in TENS group comprises putting pad electrodes on T10-L1 & S2-S4 spinal levels , then the patient could turn on the TENS device by when uterus contractions begin & turn it off when it end. She could change the frequency of impulses at pleasure. Inhalation of Oxygen will be used as a Entonox placebo. Patients in the Entonox group compress the button on the mask to inhale Entonox by start of the contractions & end it by releasing the button. Silent TENS will be used as a placebo in this group. In third group both TENS & Entonox will be used simultaneously. Main outcome measures include: Duration of first stage of delivery, pain intensity, use of analgesics, nausea & vomiting & apgar of newborn