Peptide inhibitor of C1 (PIC1) and hypothermia-enhanced complement-mediated hemolysis. Human serum (16.5%) was pre-incubated with 0.98 mM, 0.82 mM, 0.65 mM, 0.48 mM or 0.32 mM PIC1, DMSO vehicle control, or buffer control before performing the CH50-type assay at 31° or 37°C. PIC1 inhibited hypothermia-enhanced complement activation and hemolysis at 31°C for all doses tested up to 60% inhibition for 0.98 mM PIC1 compared with 31°C untreated (*ANOVA P <0.01). Increasing concentrations of PIC1 showed a significant dose dependent inhibition of hypothermia-enhanced complement activation at 31°C for all doses tested. At 31°C, 0.98 mM of PIC1 inhibited complement mediated cell lysis to a level equivalent with euthermia (37°C) (t-test P = 0.44) Data are mean ± SEM for 3 independent experiments.