The effects of intrarenal infusion of the complement-derived anaphylatoxin, C5a, upon glomerular hemodynamics were examined in the Munich-Wistar rat, a strain with glomeruli on the kidney surface. Human C5a (1.5 micrograms/min) or vehicle was infused into the left renal artery for 12 min, and glomerular capillary (PG) and Bowman's space pressures, nephron plasma flow (SNPF) afferent and efferent arteriolar protein concentrations, nephron filtration rate (SNGFR) and the glomerular ultrafiltration coefficient (LpA) determined. Human C5a infusion resulted in a reduction in SNPF due to increased efferent arteriolar resistance, and PG increased which maintained SNGFR constant. LpA was numerically lower but not significantly decreased. Infusion of porcine C5ades Arg decreased glomerular filtration rate and renal blood flow. No polymorphonuclear leukocytes were observed within glomerular capillaries of C5a infused rats, and rat leukocytes did not exhibit receptors for human C5a infused. Renal artery infusion of either human C5a or porcine C5a resulted in renal hemodynamic alterations and, as documented for human C5a, effects of C5a upon renal vascular resistance can be added to the known effect of C5a on the polymorphonuclear leukocyte.