This chapter can be used as an alternative to USP general chapter Particulate Matter in Injections 〈788〉. It specifically addresses therapeutic protein injections and related preparations, allowing use of smaller test product volumes and smaller test aliquots to determine particulate matter content, with sample-handling instructions that take into account the issues associated with the analysis of these materials. Although the methodology and limits presented in this chapter are preferred for therapeutic protein injections, the use of regulatory-acceptable alternative analytical methods with adequately developed subvisible particulate limits is acceptable.