The selection of a spectroscopie technique and wavelength for the determination of lead isotopic ratios is examined. Collisional broadening and line shift are major limitations to accurate determinations using flames or furnaces operating at atmospheric pressure and a hydrogen atmosphere is particularly bad in this regard. Direct measurements of absorption line widths (full width at half intensity) and shifts have been made at the 283.3 nm lead line in air-acetylene and air-hydrogen flames using a high-resolution monochromator. The values found are 0.00152 ± 0.00003 nm (width) and 0.00039 ± 0.00003 nm (shift) for air-acetylene and 0.00183 ± 0.00003 nm (width) and 0.00038 ± 0.00003 nm (shift) for air-hydrogen. These widths represent the total due to both Doppler and collisional broadening and the shifts in both flames are to longer wavelengths. Cathodic-sputtering is substantially free of collisional broadening and shift and provides a convenient technique for isotopic determinations.