Gelatin is a good candidate for nanoparticle preparation. An in-process study of an earlier method was performed by characterizing the gelatin species present in solution at various production stages. Gelatin nanoparticles were prepared as described by Farrugia and Groves (1999). Samples from various production stages were analysed by size-exclusion HPLC. Addition of ethanol to the initial gelatin solution removed all but the low molecular weight species. Ultrafiltration was effective at separating and purifying nanoparticles. The glutaraldehyde-metabisulfite addition byproduct present in the first ultrafiltrate was practically absent in the third ultrafiltrate and in the filtered nanoparticle and control preparations. Also, ultrafiltration of gelatin solutions removed species of low to intermediate molecular weights, leaving higher molecular weight species in the retentate. The residual soluble species following desolvation were not present in the final nanoparticle dispersion. Both the nanoparticle filtrates and the ultrafiltrate washings exhibited insignificant concentrations of eluted gelatin species. The chromatogram of a water control taken through the production process was superimposable on that of the filtered nanoparticle dispersion, indicating that soluble gelatin species present post-desolvation were absent following cross-linking and neutralisation. A possible explanation is that the glutaraldehyde crosslinked the residual soluble gelatin onto the surface of existing nanoparticles.