In order to test the role of limestone in producing anomalously old radiocarbon ages in land-snail shells, 14C analyses were performed on shell carbonate of modern land snails from limestone and nonlimestone areas of Jamaica. No anomaly was found in snails from the nonlimestone area, implying that such material is suitable for radiocarbon dating. Snails from limestone areas produced variable anomalies of as much as 3,120 yr due to incorporation of 14C-free limestone into shell carbonate. All rock-scraping snails and most leaf-litter–feeding snails from limestone areas showed anomalous 14C contents. Because of the variability in 14C content even within species, no standard correction factor for limestone anomaly can be applied. However, dating error can be minimized by selecting ecologically appropriate species or by comparison of analyses of several fossil species, within a stratum, to their modern counterparts.