This step-by-step video clearly demonstrates the correct technique for the execution of the manual assay for the presence FVIII inhibitors. Supplementing the Lab Manual written protocol (Section 28), it also explains the theory behind the assay, details the important reagents, discusses the challenges posed by limited resources, and works through the plotting and interpretation of a series of typical diagnostic cases including immediate acting and time-dependent inhibitors. The accompanying searchable transcript links to the individual sections of the video. A blank FVIII inhibitor assay record sheet and log-linear graph paper are also provided for free download.