Laser-Induced Incandescence (LII) technique is a powerful tool to measure concentration and size of soot particulate. In this work LII measurements are performed in different experimental conditions and compared with the ones derived by using a commercial aethalometer. This instrument allows to obtain the on-time concentration of optically absorbing aerosol particles by measuring the attenuation of 800 nm wavelength light through a quartz fiber filter. The filter is blackened over time with the aerosol picked up inside the instrument at controlled flows. Measurements are carried out with one second time-resolution. Absolute measurements in the ng/m3 range are derived for the particulate concentration. As for Laser-Induced Incandescence, soot particles are sampled in a test cell, consisting of a pyrex tube. The IR beam of a Nd:YAG laser (6 Hz, 200 mJ/cm2) is properly aligned within the tube. The LII signal is detected at two wavelengths (530 nm and 700 nm) with PMT modules coupled with interference filters. A fast digital oscilloscope, triggered by the laser Q-switch pulse, is used for data acquisition and storage. The two sets of measurements are carried out at the exhaust of a soot generator (fuelled by methane) and of a diesel engine as well as in ambient air conditions (office and laboratories). In this way, a wide range of soot load and particulate of different nature are investigated.