This study sought to extend validation of a cyclodextrin based extraction method for the assessment of PAH-biodegradation potential to complex multi-contaminant matrices. To this end, four reference materials (RMs) were produced by blending, in different proportions, soils impacted with diesel, lubricating oil and spent oxide. These reference materials had modest Sigma PAH (16 US EPA) concentrations that ranged from 5.6 +/- 0.5 to 44.4 +/- 4.5 mg kg(-1). However, extractable petroleum hydrocarbon (EPH) concentrations were comparatively high (up to 2520 +/- 204 mg kg-1). To complement these RMs, two further soils from a municipal gas plant (MGP) with highly elevated concentration of PAHs ranging from 877 +/- 52 to 2620 +/- 344 mg kg(-1) were also tested. Results showed, regardless of matrix complexity, that PAH biodegradation within the four RM substrates, and two MGP soils correlated well with biodegradation predicted by hydroxypropyl-5-cyclodextrin (HPCD) extraction. (C) 2008 Elsevier Ltd. All rights reserved.