Pulsed magnetic fields are used to study a variety of self-assembled semiconductor nanostructures. We illustrate the power of the technique with two recent examples. In the first, we study confinement in InAs quantum dots on (1 0 0) and (3 1 1)B oriented GaAs substrates as a function of InAs coverage. We demonstrate that Stranski-Krastanow growth occurs for (1 0 0) substrates, but show that for (3 1 1)B substrates there is no such transition-rather the dots evolve from fluctuations in the wetting layer. In the second example, we investigate the Coulomb binding of 'free' electrons to holes confined to type-II GaSb/GaAs quantum dots. We find that at low laser power the electrons are repelled from the dots (by strain), but that by optical pumping the dots may be multiply charged, attracting the electrons, and more than doubling the binding energy. (C) 2004 Elsevier B.V. All rights reserved.