Lead concentrations have been analyzed on a 223 yr profile through the aragonitic skeleton of the reef-building Caribbean sclerosponge Ceratoporella nicholsoni by using laser-ablation inductively coupled plasma–mass spectrometry. A parallel study of the δ13C distribution in the skeleton validates the previously established mean annual growth rate of 230 µm/yr, at least for long-term important environmental changes. The Pb trend in the specimen displays a general increase from 0.30 ppm ca. A.D. 1760 to 2.15 ppm ca. A.D. 1984; a major threefold increase occurred after 1930. This Pb profile is analogous to results acquired from ice or coral cores and clearly highlights the potential of sclerosponges as a new proxy of environmental changes for time series extending over several centuries.