Small radiation packs containing nuclear emulsions and plastic foil detectors carried by the Apollo XI astronauts furnished a detailed record of the astronauts' radiation exposure. The exposure was found to result mainly from nuclear particles, with electrons and gamma rays contributing only about 15% to the total dose equivalent. A mission dose of 201 mrads corresponding to 402 mrems was found. By far the largest part of the dose was due to trapped protons encountered in two passes of the radiation belt on translunar and trans-Earth injection. Orientation of the plane of orbit to the geomagnetic equator was extremely favorable on both passages, resulting in very peripheral crossings of the inner belt. Mission doses on lunar missions in general, therefore, can be expected to be substantially larger. This has been borne out subsequently by Apollo XIV, which had to go through the core of the inner belt on translunar injection and accumulated a total mission-dose equivalent slightly above 1,000 mrems.