Abstract: Although wastewater discharges of CN- have been regulated for many years, lack of accurate methods to quantify different forms of CN- requires dischargers of wastewater which contains less toxic or non-toxic forms of CN- to use overly aggressive, expensive treatment methods or take site-specific, risk-based approaches to revise CN- criteria. The CNA method (CN- amenable to chlorination) is the most accurate USEPA-approve method to measure compliance with free CN- standards or limits; however, USEPA has proposed approving other methods to measure available CN- at lower concentrations and with better precision (flow injection and ligand-exchange methods). Since methods to measure compliance do not differentiate between free, weakly complexed, or strongly complexed CN-, selecting cost-effective treatment methods for metal-complexed CN- is difficult. Although wastewater may contain only strongly complexed forms of CN-, which are less toxic than free CN-, dischargers must treat wastewater with the assumption that any CN- detected is of the most bioavailable, toxic form. New, revised CN- anal. methods being developed by USEPA and the ASTM are encouraging. A USEPA-approved method to measure free CN- in wastewater, receiving water, or groundwater would improve efforts to characterize samples and facilitate accurate input to fate and transport assessments.