This article presents tools for soot diagnostics at elevated pressure. Investigations on laser-induced incandescence (LII) are shown in a laminar premixed ethylene/air flame at pressures up to 5 bar in a recently constructed high-pressure burner. The LII signal decay was compared to results of a numerical model taking into account the pressure-dependent heat transfer. Required input parameters for the model are the peak particle temperature as well as the gas-phase temperature. The peak particle temperature was measured using two-color LII, the gas-phase temperature was determined with multi-line NO-LIF thermometry. Model results are shown where the pressure-dependence of the LII signal intensity is investigated. It shows that intensities decrease with increasing pressure which has an important impact on the transfer of the calibration of LII for soot volume fraction measurements from atmospheric pressure to high pressure. A practical application of LII in a Diesel engine is shown. Here, particle sizes were obtained from in-cylinder measurements with time-resolved LII.