Pulsed field gradient (PFG) nuclear magnetic resonance (NMR) was applied to study self-diffusion in a ternary blend containing equal molar volumes of the homopolymers poly(dimethylsiloxane) (PDMS) and poly(ethylethylene) (PEE), and the nearly symmetric PDMS-PEE diblock copolymer. The blend forms a bicontinuous microemulsion (BmuE) below similar to83 degreesC, while it is in the disordered state at higher temperatures. PFG NMR has also been applied to the individual components of the blend. In the blend, we find one diffusional process in the disordered state and two diffusional processes in the BmuE state. The fast process in the BmuE is due to the diffusion of the PDMS homopolymers through the BmuE. This diffusion is ten times slower than that of bulk PDMS at the same temperature, indicating restricted diffusion of PDMS in the BmuE. The diffusion coefficient of the slower process in the ternary blend is slightly increased compared with bulk PEE. It is tentatively assigned to PEE self-diffusion. The changes in homopolymer diffusivities are semiquantitatively explained in terms of a model taking into account the tortuosity of the BmuE as well as the fast exchange of homopolymers between the domains and the difference in viscosities of the PEE and the PDMS domains. Our results are compared with data obtained previously on the identical sample with dynamic light scattering experiments [T. L. Morkved , Faraday Discuss. 112, 335 (1998)].