The electron spectrum arising from internal conversion in 169Tm has been examined as a function of the chemical environment. The 169Er ions were imbedded after passage through an isotope separator into a variety of targets including tungsten metal, WO 3 and Tm 2O 3. The electron spectra were measured with a double-focussing electron spectrometer. The relative intensities of the converted electrons with the exception of the outermost P I shell were insensitive to the chemical media. The analysis gave M I 100, M II 37 ±1, Rm III 38±1, M V 0.9 ± 0.2, M V 1.0±0.2, N I 22.1±0.6, N II 6.4±0.3, N III 7.6±0.2, N IV,V 0.20±0.02, O I 3.7±0.1, O II, III 2.08±0.06. This is in agreement with theory based on an M1 transition with 0.108% E2 admixture. The intensity of the P I shell, however, was found to be dependent on the chemical surroundings. The ratio of P I/O I intensities were 0.056±0.007, 0.035±0.006, and 0.030±0.006, respectively, for W, Tm 2O 3 and WO 3. This indicates that the P I conversion in the oxides is 38% (Tm 2O 3) and 46% (WO 3) lower than in the metal. The internal conversion coefficients were compared with electron densities obtained from relativistic wave functions for Tm and Tm ions. From this comparison, it was possible to estimate the changes in electron densities at the nucleus. A discussion is made of the importance of these electron density measurements in evaluating Mössbauer isomer shifts. The transition energy is found to be 8.401±0.008 keV.