An inexpensive, high-speed densitometer made from an Apple II computer, a black-and-white video camera, and an image digitizing board is described. By supplementing the computer with a very fast coprocessor, one can obtain a measurement of a typical thin-layer spot in 30-40 s. Only minimal electronic expertise is required for assembling the system from the commercially available components. Coefficients of variation for multiple readings of a single 500-ng spot of charred lipid were about 0.5%. For lipid spots weighing 250 to 2000 ng, a second-order relationship between weight and density reading was obtained with a correlation coefficient of 0.998.