Project Star Dust was undertaken to prepare a mathematical model of atmospheric mixing and transport which can be used to predict stratospheric hold-up and ultimate patterns of deposition on the surface of the earth of radioactive debris injected into the stratosphere by nuclear weapons tests, by burn-up on re-entry of nuclear power packs for earth satellites, or by other causes. Information on several atmospheric tracers is being used to guide the selection of values for the various meteorological parameters included in the model. Among these tracers are ozone, water vapor and such radionuclides as strontium-90, tungsten-185, rhodium-102 and beryllium-7, which have been introduced into the stratosphere by nuclear weapons tests or by natural atmospheric processes. Work on the Star Dust model of atmospheric mixing and transfer has passed the stage of initial mathematical studies and has entered the stage of computer testing and modification of parameters. Two very preliminary models have been tested on a CDC 1604 computer and have been checked against HASP tungsten-185 data. They have shown that the observed spread of the tungsten-185 clouds can be fairly well duplicated even by the simplified model based only on eddy diffusion. More complicated models are now being prepared and tested.