The purpose of this report is to describe the occurrence of and trends in selected sediment-associated contaminants in age-dated sediment cores from four sites in the Texas part of Caddo Lake. Radionuclides were used to age date the sediment layers in the cores, which makes possible evaluation of changes in contaminant concentrations over time. The report explains the age-dating process and associates dates of deposition with successive intervals in each core. Concentrations of selected organochlorine compounds, polycyclic aromatic hydrocarbons (PAHs), and trace elements are compared to sediment-quality guidelines that reflect relative sediment toxicity to aquatic biota. Trends based on contaminant concentrations in intervals of core sediment were tested for statistical significance. Potential sources of contaminants, particularly mercury, are discussed.