The objective of the study was to evaluate the effectiveness of various methods of RNA extraction from feces of diarrhoeic piglets to diagnose rotaviral infections by the polymerase chain reaction (PCR). The most effective among the four methods of extraction appeared to be the extraction of RNA with quanidine thiocyanate followed by purification on glass powder. This method also enabled an effective removal of unspecific inhibitors affecting enzymatic activities in RT-PCR reactions. By using this method products of PCR reaction were obtained in 9 out of 10 positive samples in ELISA while positive reactions were absent in 5 negative samples. This type of extraction is easy to handle and not time-consuming and it enables to simultaneously prepare a lot of samples.