High-LET particle radiation was registered in nuclear track recording plastic dosimeters worn on the wrists of Skylab astronauts and located in a heavily shielded film vault. The mission-average planar flux of high-LET particles with LET ≥ 100 keV/μm tissue has been determined to be 2.7 ± 0.6 particles/cm2 day 2 pi sr and 0.34 ± 0.4 particles/cm2 day 2 pi sr, respectively, for the nine astronauts and for the film vault (drawer F). Comparison of results representative of a wide range of shielding depths reveals that the magnitude and slope of the integral LET spectrum of high-LET particles inside spacecraft are proportional to the amount of shielding.