4 mM melittin solution in 0.05 M sodium phosphate buffer at p2H 7.0 and 30 degrees C was shown by ultracentrifugation to contain tetrameric melittin. Using the spectra of this species and the previously characterized monomeric melittin as references, high-resolution 1H-NMR at 360 MHz was used to investigate self-aggregation of melittin at variable temperatures, pH and ionic strength. The NMR parameters show that the spatial structure of aggregated melittin is different from monomeric mellitin in aqueous solution but resembles closely the conformation adopted by melittin bound to detergent micelles. Comparison of melittin bound to different detergent micelles and self-aggregated melittin in different aqueous media indicates that the mellitin monomers adopt similar conformations in all these systems. The present data suggest that melittin assumes an amphiphilic spatial structure which is stabilized both by the formation of mixed micelles with detergents or by self-aggregation.