This report details the development of a portable device to measure the cleanliness and stability of diesel fuels in both bulk and vehicle fuel cell storage. Both an initial laboratory prototype and a portable field unit are discussed. The monitor evaluates the cleanliness of the fuel by first filtering the fuel and then determining the amount of particlulates on the filters using a contaminated filter measuring device. The filters are rated by measuring the amount of light which passes through the filters to estimate the amount of particulates based on a calibration chart. A measure of the stability of the fuel is obtained by aging a sample of the fuel at 150 C for 1.5 hours and determining the amount of sediment formed. Based on preliminary correlations of 150 C test data with ASTM D 2274 accelerated stability data, 'go/no-go' values of 4,4-6, and6 mg/100 m1 have been suggested for rating a fuel's stability as good, marginal, or bad, respectively. Improvements to the diesel fuel quality monitor have been identified and are being investigated. A field test program to demonstrate monitor utility/effectiveness is planned for initiation in late 1981. In addition, a commercially available portable unit to measure particulate contamination is described and compared to the Army field test unit.