During the period 2018-2020, studies were conducted to determine the parameters of protostrongylid infectiоn in intermediate hosts in pastures in the Western Rhodopes and Pirin Mountains. Of the eleven snail species identified, four were registered as intermediate hosts of protostrongylids. On the studied pastures – Mugla, Zabardo and Vihren SE, protostrongylid larvae were detected in Xerolenta obvia at the first and second sites and in Xerolenta macedonica, Cattania polinscii and Cattania haberhaueri at the third site. The differences in the periods of maximum risk of infection observed in the present study and the data of other authors are due to the high altitudes at which the studied pastures are located. Тhe high values of certain infection parameters observed in summer are likely due to the significantly higher amount and frequency of precipitation in the mountainous areas, combined with favorable temperatures, which in a large part of the period are in the optimal range.