Magnetic resonance and u.-v. spectroscopic studies of spin probes solubilized in sodium dodecyl sulphate (SDS) micelle solutions give information concerning the position of the spin probe within the micelle and molecular dynamics in micelle solutions. Spin probes have rapid motion (τ–1∼ 1010 s–1) within the micelle, but motion is more restricted than in water or dodecane (τ–1∼ 1011 s–1). The frequency for the exchange of spin probes between micelles and surrounding solution is in the range 104–106 s–1. Spin probes were found to be located near the surface of the micelle. The time averaged micellar environment of: [graphic omitted] has the dinitrophenylhydrazylgroup in the surface of the micelle, probably adjacent to the sulphate groups, and the nitroxide group penetrating a small distance into the hydrocarbon core of the micelle. In contrast to its behaviour in other systems, the nitroxide [graphic omitted] is located in the surface of the micelle, probably adjacent to the sulphate head groups. The nitroxide [graphic omitted] is incorporated in the micelle, similar to SDS.