When combined with high index constrast slabs in which light can be efficiently guided, microfabricated two-dimensional photonic bandgap mirrors provide us with the geometries needed to confine light into extremely small volumes. We show that these high Q cavities now make it possible to define microcavity lasers which function at room temperature and have mode volumes as small as 2.5 (λ/2nslab)3 or 0.03 μm3 in InGaAsP emitting at 1.55μm.