In order to obtain a microemulsion that is stable at skin tempeature, the regions of existance of microemulsions of water and isoproptyl myristate were studied as a function of hydrophilelipophile balance (HLB) of nonionic surfactant mixtures. The microemulsion dissolves large amount of the local anaesthetic lidocaine. The amount of dissolved lidocaine in the microemulsion was proportional to the isopropyl myristate content and limited to its solubility in this solvent. The addition of lidocaine lowered the phase inversion temperature (PIT) of the system and increased the temperature range for microemulsion stability. The structure of the microemulsion, as investigated by proton Fourier transform pulsed-gradient spin-echo NMR spectroscopy, was found to be bicontinous. The physico-chemical properties of the microemulsion as well as the low toxicity of its components result in formulation intendend for topical administation.