The effect ofthe Prostaglandin F2Α. (PGF2Α.) upon the myometrium of cranial and caudal segments from the right (RH) and Ieft (LH) uterine homs, as well as on the right (RUB) and Ieft (LUB) segments ofthe uterine body in vitro, was studied in non-pregnant adult alpacas. The results are expressed as percent of maximum tension obtained by depolariz.ation with 50 mM ofCIK. Accumulative doses of l.89 × 10-7 M, 5.66 × 10-1 M, 9.41 × 10-7 M and l.31 × 10-1 M of the last concentration of Prostaglandin F2Α, produced muscular myometrium contraction in all segments as follows: in RH 68.63±9 .32, 65.42± 1 l. 73, in LH56.12±8.46,47.72±6.25, RUB 39.72±6.67 and LUB46.97±4.29forthe firstdose; in RH 76.18±2.91, 75.97±13.04,inlR70.30±7.47,66.48±6.02,RUB48.58±7.56andLUB57.27±6.49 fortheseconddose; in RH 83.53±5.51, 85.15±9.32, in LH 79.35±11.35, 73.17±5.94, RUB 45.20±5.92 and LUB 62.50± 7 .20 forthe third dose; and finally, in RH 78. 84.53± 14.68, inLH 70.35±11.76, 61.78±3.70, RUB40.32±6.34 andLUB 59.33±12.08 forthe fourthdose, respectively. In conclusion, contraction frequency (%) was greater in the cranial and caudal segments of the right and left uterine horns (P<0.05) than in the uterine body segments. Maximum contraction levels were achieved with the third accumulative dose of Prostaglandin F2Α., but these did not exceed the contraction frequency (%) obtained withClK.