Twenty monodisperse polystyrene latexes were made by seeded emulsion polymerization in the MLR-SEP flight hardware on theSTS-3 and STS-4 flights of the Columbia and the STS-6, STS-7, and STS-11 flights of the Challenger. Two polymerizations were small-particle-size controls; the other eighteen were of large particle size. Of these, six failed: four on STS-4 owing to malfunction of the flight hardware; one on STS-6 owing to a broken wire; one on STS-11 owing to a broken stirrer shearpin. Nine monodisperse latexes of 4–30 μm size had narrower particle size distributions than the ground-based controls. The 10 μm STS-6 latex and the 30 μm STS-11 latexes were accepted by the National Bureau of Standards as Standard Reference Materials, the first products made in space for sale on earth. The polymerization rates in space were the same as on earth within experimental error. The flight polymerizations produced only negligible amounts of coagulum; the ground-based control polymerizations produced increasing amounts with increasing particle size, so that these controls were discontinued after the STS-7 experiments. These results confirmed the original rationale of the experiments that polymerization in space would give more uniform large-particlesize monodisperse latexes with less coagulum by: 1. the better uniformity of all 5 μm or larger flight latexes; 2. the more perfect sphericity of the 10 and 30 μm particles; 3. the smaller number of offsize larger particles; 3. the negligible amounts of coagulum; 4. the broadening of the particle size distribution and the formation of more larger offsize particles during the completion on earth of the polymerization of the partially converted STS-4 flight latexes.