Commercially pure titanium components in medical devices are commonly joined using pulsed laser welding because of the precision, low heat input and low thermal distortion it affords. Despite the importance of this technique in structural components, such as dental prosthesis, there is still a limited understanding of the factors which affect the weld metallurgy. In this study the effect of O, N and Fe on the weld metallurgy, as both external and bulk contaminants, is investigated. The results indicate that Fe has the most pronounced effect on the nature of the allotropic beta-I +/- phase transformation, suppressing the massive transformation and encouraging the formation of martensite. This finding is in contrast to the effects of O and N which are usually the subject of studies reported in the literature. Whilst O and N do cause more hardening than Fe, this seems to be mainly through more pronounced solid solution strengthening. The study also demonstrates the inadequacy of relying on ASTM grades to predict weld properties and the need to adequately characterise the base alloys.