In the late 1960s, Ian Kaplan created a state-of-the-art laboratory for isotopic analysis of biogenic elements in returned lunar samples. Interpretation of the large resulting database led to important insights into both physical/chemical processes on the lunar surface and the flux of solar-wind and meteoritic material onto the lunar surface. Abundance and isotopic data for sulfur reveal a dynamic balance between influx of meteoritic sulfur and loss of sulfur through impact heating and/or solar-wind sputtering. Data for nitrogen apparently record long-term variations in composition of the solar wind, though this remains controversial. If correct, this conclusion represents a profound challenge to contemporary understanding of solar history and processes. Carbon in the lunar regolith shows significant isotopic variability whose cause(s) remain presently unknown.