Lard from 26 sources was stored in glass jars at 26.7 °C (80° F) until definitely rancid. Spoilage was evaluated at two-week intervals by chemical tests and odour ratings. Correlation coefficients between odour scores and the logarithms of chemical test values were: iodometric peroxide, −.90; alpha-dicarbonyl test, −.85; Stamm test −.82; Kreis test −.81; ferrometric peroxide, −.80; fluorescence,.79; free fatty acids, −.10. Association between chemical measurements was greatest between alpha-dicarbonyl and iodometric peroxide values (r = 97). As peroxides are not thermostable, the measurement of the stable alpha-dicarbonyl compounds, although less precise, is considered the best available chemical method for assessing rancidity.