A uniform log-normal pattern of frequency distribution of cestodes and nematodes in poikilothermic and homeothermic hosts from Garhwal Himalayan ecosystems by size and weight classes during infection period indicates subtle relationship to the range of variation in the earth’s environment. The frequency of occurrence of the rodent cestodes followed a definite, ordered, mathematical distribution. This conclusion presumably reflects that a number of random processes in the host-parasite interaction are superimposed and the environmental interplay has resulted in the log-normal distribution of parasite species inRattus rattus of high altitude in India.