A possible contribution of solar energetic particle events to the production of cosmogenic 10Be and 14C in the atmosphere is studied. The solar particle effect is negligible in the 14C data, but extreme events may be detectable in high-resolution 14C data. Although the overall effect is small in the 10Be data, strong events may contribute notably on the inter-annual time scale. In combination with the 11-year solar modulation of galactic cosmic rays, it may lead to an intermittent 5.5-year periodicity, which is seen in high resolution 10Be data. We have identified ten episodes during 1750--1950 when 10Be may hold signatures of strong solar proton events. This opens a new possibility to study extreme solar particle events in the past using high resolution cosmogenic isotope data.