Normal guinea pig serum is tested for complement activity and certified to possess functional classical and alternative pathways of activation. GPS was prepared from male mixed breed guinea pigs. Each sample of blood was collected without anticoagulants and after coagulation the liquid portion was separated by centrifugation. Serum was filtered through a 0.22 µm filter, aliqoted and frozen at -80 o C. Guinea pig complement was used in the first few decades of complement research because it exhibits 4 to 5-fold higher titers of classical pathway activity against EA in CH50 assays than human serum. In addition, a C4 deficient line of guinea pigs (CompTech product C4-D guinea pig serum #A305) was discovered in 1970 allowing unique research to be done (e.g. the discovery or re-discovery of the alternative pathway) (Ellman, L., et al. (1970)). Later a line of C2 deficient guinea pigs was also discovered (Bitter-Suermann, D., et al. (1981)). In addition, GPS is considerably more stable that mouse or rat complement making it easier to work with. All testing for complement activity in GPS was performed on the once frozen and subsequently thawed samples to guarantee that the functional activity reported is what customers will receive when their samples are thawed. Complement activity is stable for several years if GPS is stored at -70 o C or below continuously. Guinea pig complement is not as stable as human complement in normal human serum and some degradation of activity may be observed if the GPS is allowed to remain thawed for more than a few hours even if it is kept on ice. While it is better to freeze it overnight below -70 oC , some loss of activity may occur following this additional freeze thaw cycle. (For complete description see link...)