Comparison of ribonucleic acid (RNA) isolation kits analysed by real-time polymerase chain reaction. Results of RNA isolation with the different kits and for the different cartilaginous tissues are compared by analysing the differences in aggrecan gene expression between duplicate samples: a) for the RNeasy Lipid (dark orange) and Fibrous (light orange) kits; and b) for TRIzol. Tissues homogenised with the same method are pooled. Data are presented as mean and standard error of the mean. Note the linear scale for graph (a) and the logarithmic scale for graph (b). (AC, articular cartilage; M, meniscus; AF, annulus fibrosus; NP, nucleus pulposus.)