This invention relates to a multiplex PCR assay capable of screening or detecting the relevant microbial organism specific to Mycobacterium tuberculosis, Toxoplasma gondii, pathogenically important fungii and cytomegalo virus (CMV) in a sample, comprising a reaction mixture of a combination of 4 sets of primers, one of said primer for detection of Mycobacterium tuberculosis, a second of said primer for detection of Toxoplasma gondii, a third primer for the detection of pathogenically important fungi and a fourth primer for the detection of CMV, said primers being compatible to each other.