Regarding risk evaluation of complex mixtures, the Working Group discussed the following topics: evaluation of the mixture as a whole, fractionation of the mixture, identification of the 'top ten' chemicals, and composite standards. It was concluded that no standard methodology for hazard identification and risk assessment of complex mixtures yet exists, but assessment of complex mixtures must proceed, using all available information,methods, technology, expertise and experience. The development of a decision tree for tackling complex mixtures was recommended, and the need to move forward with instituting standards for mixtures, especially in job-oriented situations, was emphasized.