The partitioning and hydration of 2,3-butanedione and 2,3-pentanedione have been measured in sodium dodecyl sulfate micelles and AOT reverse micelles. In the latter system, the incorporation of both compounds to the micellar pseudophase is proportional to the amount of water at water/AOT ratios higher than 9. This result is interpreted in terms of a dominant incorporation of the diketones to the water pools. With regard to both solubilization and hydration, the water of the reverse micelle pools behaves nearly as bulk water (at water/AOT ratios higher than 9). The addition of sodium dodecyl sulfate to an aqueous solution of 2,3-pentanedione decreases the extent of hydration of the diketone. Measurement of the quenching of 2,3-pentanedione fluorescence by iodide allows an evaluation of the extent of solubilization in the micellar pseudophase. From these data and the changes in absorbance of the alpha-dicarbonyl band with the surfactant concentration (which is a measure of the degree of hydration) the partition constant of the hydrated and nonhydrated forms of 2,3-pentanedione are evaluated. The results obtained indicate that the hydration of 2,3-pentanedione molecules bound to sodium dodecyl sulfate micelles is nearly 4.6 times less efficient than in bulk water.