SERUM chemistry of non-pregnant (Group I) and pregnant (Group …. II) female Rattus rattus (n=389) collected alive from wild conditions in rat traps was investigated in different weight groups (A: 50-100gm, B: 100-150gm and C: 150-200gm) under uninfected and infected (Trypanosoma and Cysticercus) conditions. Groups I and II were further subdivided into four subgroups each, a: Uninfected rats, b: T. lewisi infected rats, c: C. fasciolaris-infected rats, d: T. lewisi and C. fasciolaris-infected rats. A significant maximum fall of 38.01% in glucose was recorded in pregnant rats of Group IIb (weight category B). Changes in cholesterol were insignificant in most of the groups except Group IIc (weight category B) where the fall was maximum (25.32%). Total serum protein (TSP) changes were again insignificant in most of the groups except in weight categories B of Group IIb showing 18.54% rise and Group IIc showing 22.62% fall. Changes were significant (P<0.05) in hemoglobin in parasitized rats showing a maximum fall of 36.63% in Group IIb (weight category B). The results infer that glucose and hemoglobin are the most vulnerable biochemical constituents to parasitism and that older (weight category B and C) pregnant rats (Group II) and rats with dual infection (Group IId) exhibit greater changes in their biochemical constituents.