THE radiative properties of an atomic or molecular system may be altered significantly in the presence of coherent optical scattering1,2. In the course of investigating the radiative properties of a laser dye dispersed in a strongly scattering medium (a colloidal suspension of titanium dioxide particles), we have found that the emissions from such systems can exhibit spectral and temporal properties characteristic of a multimode laser oscillator, even though the systems contain no external cavity. The threshold excitation energy for laser action is surprisingly low. We suggest that these composite systems might find applications in laser instrumentation and photonics.