The application of mixtures of coal fly. ash (CFA) and cement for fixation of toxic metals is considered. It is shown that mixtures of CFA and cement can be effectively used for solidification and stabilization (So/St) of aqueous solutions of toxic metals. The ratio of fly ash to cement, FA/C, has a dominant effect on the strength and the acid neutralization capacity (ANC) of the solidified monolith. The economic incentive of using higher FA/C ratios and the requirements of minimum strength indicate a preferable working range for FA/C between the 80/20 and 95/5 levels. Results of prolonged curing and setting times show a considerable increase in strength which suggests the option of a narrower 90/10 - 95/5 working range. At these high values of FA/C, the ANC is mostly determined by the CFA rather than by the cement. For relatively high ANC levels, the fast neutralization of the mild acids used in the standard EP EPT and TCLP tests renders them unsuitable for characterization of the quality of So/St processes. A new testing procedure, with the leachant set at pH 0.7, provides the means to characterize the quality of monolith samples regarding their metal fixation against the action of acids. The Characteristic Composition Transition Point (CCTP) and the Characteristic pH Transition Point (CPTP) are defined as indicators of the quality of the So/St process and its products. Higher CCTP and lower CPTP indicate better fixation qualities. Finally, the results of leaching tests can depend on the relative rates of acid neutralization and metal dissolution. Fast acid neutralization and slow leaching during the test decrease the level of leaching which appears as a lower metal leachability, whereas slow neutralization and a fast leaching rate produce the reverse effect.