The present invention relates to a method for detecting and differentiating PCV infections in a biological sample taken from a pig which involves amplifying a fragment from an extracted nucleic acid; digesting the fragment with a suitable restriction enzyme such as the unique NcoI restriction enzyme; forming a restriction fragment length polymorphism pattern; and then detecting the presence or absence of a PCV isolate. The invention further concerns the new oligonucleotide primers for differentiating PCV infections comprising a nucleotide sequence selected from the group consisting of MCV1 having a nucleotide sequence set forth in SEQ ID NO:1 and MCV2 having a nucleotide sequence set forth in SEQ ID NO:2. Moreover, this invention provides a novel kit for detecting and distinguishing PCV infections that includes the new oligonucleotide primers and the suitable restriction enzyme.