This study quantified and described the distribution of the 36 moulds that make up the Environmental Relative Moldiness Index (ERMI). As part of the 2006 American Healthy Homes Survey, settled dust samples were analysed by mould-specific quantitative PCR (MSQPCR) for the 36 ERMI moulds. Each species’ geographical distribution pattern was examined individually, followed by partitioning analysis in order to identify spatially meaningful patterns. For mapping, the 36 mould populations were divided into disjoint clusters on the basis of their standardised concentrations, and First Principal Component (FPC) scores were computed. The partitioning analyses failed to uncover a valid partitioning that yielded compact, well-separated partitions with systematic spatial distributions, either on global or local criteria. Disjoint variable clustering resulted in seven mould clusters. The authors concluded that the 36 moulds and ERMI values themselves were found to be heterogeneously distributed across the United States of America (USA).