Focused ion beams of Be and Si were used to expose the following resists: PMMA, HEBR‐214, KTI 820, and Microposit 2400. The resist thickness remaining for various development times was measured. For example, the minimum dose of 200 keV Be ions needed to expose 6800 Å thick PMMA varied from 7×1012to 2×1013ions/cm2depending on development time. HEBR was found to act as either a positive or negative resist depending on dose. Exposures were also carried out in resist whose thickness exceeded the ion range. The effective PMMA exposure ranges of 200 keV Be ions and 200 keV Si ions were found to be 1.2 and 0.45 μm, respectively.