As the area of nucleic acid based technologies develops, so will our understanding of how structural variations in DNA and RNA pathogens are associated with disease. The overall goal of this thesis is the development of broadly targeted measurement techniques for variable viral RNA by Real-Time PCR (here referred to as quantitative reverse transcriptase PCR, QRT-PCR). In papers I & II, broadly targeted and specific QRT-PCRs were used to study expression of endogenous and exogenous betaretrovirus sequences in human tissues. Results from human tissues demonstrated endogenous betaretrovirus expression in a tissue-specific manner, highest in reproductive tissues. Despite the high sensitivity, no exogenous betaretrovirus was found in human breast cancer samples. The limits of primer and probe degeneracy for detection of a diverse set of retroviral sequences was evaluated. These methods are useful for further investigations on the pathophysiological contribution(s) of endogenous betaretrovirus and to investigate whether an exogenous betaretrovirus is involved in human breast cancer. In papers III & IV, we developed and applied broadly targeted one-step QRT-PCRs for influenza viruses and coronaviruses. In addition to the generic primers, two novel probe design strategies were used in order to be able to broadly amplify these diverse sets of viruses: A triplex system for simultaneous detection and quantification of influenza A, B and C (3QRT-PCR and further developed 3QRT-PCR-MegB; where MegB stands for MegaBeacon) based on TaqMan® and MegB probes, and a pan-CoV QRT-PCR, based on three TaqMan® probes i.e., degeneracy was distributed on three probes. Probe fault tolerance was thus increased in two ways, either with short probes with/without locked nucleic acid (LNA) nucleotides concentrated to conserved stretches, or with long probes (MegB), compensating mismatching positions with many matching ones. Clinical samples, negative by antigen detection with immunofluorescence (IFA), were influenza A positive with 3QPCR-MegB. Avian pooled samples, negative with an earlier pan-CoV QPCR, came out positive with the triple-probe system. Assay evaluation with clinical samples and reference strains revealed good clinical diagnostic potential. Thus, the thesis describes several strategies to counteract sequence variation of RNA viruses and describes a set of broadly targeted QRT-PCRs useful for scientific screening or diagnostics of betaretroviruses and respiratory viruses.