We simulate lattice QCD with a finite chemical potential for isospin and2-colour QCD with a finite chemical potential for quark number.For large chemical potentials both these theories have a superfluid phasewhich is the analogue of the colour superconducting phase expected forQCD at large baryon-number chemical potential. We measure the dependenceof the lattice QCD finite temperature transition on the isospin chemicalpotential for small chemical potential where the dependence on isospin andquark-number chemical potentials is expected to be identical, and at largechemical potentials where the pion condensate evaporates.