The study of the role of caspases during apoptosis, but also during non-apoptotic developmental and signalling processes, is hampered by the lack of specific assays to measure the activity of single members of the caspase family. Neo-epitope antibodies against the active forms of caspases are available and can be used in immunohistochemical and Western blotting applications. However, the presence of active caspase fragments does not necessarily correlate with proteolytic activity, since the proteases could be bound to either endogenous or exogenous inhibitors, which is especially problematic in high-throughput screening campaigns aiming to identify caspase inhibitors. Another method using immunoprecipitation with biotinylated zVAD, on the other hand, is specific to active caspases, but quantitation relies on the efficacy of immunoprecipitation and Western blotting [23] .