Morphologically, nine different slow-growing protoclones were screened from regenerated protoplasts of heterokaryotic Agaricus bisporus. As such, the present study is the first report on differentiating homo- and heterokaryotic protoclones using random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) markers. Among 80 primers tested, the seven ISSR and seven RAPD primers selected for the analysis generated a total of 94 ISSR and 52 RAPD fragments, respectively. The ISSR fingerprinting also detected more polymorphic loci (38.29%) than the RAPD fingerprinting (34.61%). A principal coordinate analysis (PCA) was employed to evaluate the resolving power of the markers as regards differentiating protoclones. As a result, the mean polymorphism information content (PIC) for each marker system (i.e., 0.787 for RAPD and 0.916 for ISSR) suggested that ISSR is more effective for determining polymorphisms. The dendrograms constructed using RAPD, ISSR, and an integrated RAPD and ISSR marker system were highly correlated with one another as revealed by a high Mantel correlation (r= 0.98). The pairwise similarity index values also ranged from 0.64 to 0.95 (RAPD), 0.67 to 0.98 (ISSR), and 0.67 to 0.98 (RAPD and ISSR), whereas the mean similarity index values of 0.82, 0.81, and 0.84 were obtained for the RAPD, ISSR, and combined data, respectively. As there was a good correspondence between the RAPD and ISSR similarity matrices, ISSR would appear to be an effective alternative to RAPD in the genetic diversity assessment and accurate differentiation of homo- and heterokaryotic protoclones of A. bisporus.