The interactions of breed, season and environmental temperature influencing reproductive activity in Indian sheep breeds have been studied so far in some detail only with respect to the physical characteristics of the semen (Sahni & Roy, 1969; Mittal & Ghosh, 1979). The literature on the influence of these factors in determining the concentration of some of the important chemical constituents of ram semen is scanty, except for two recent reports by Nivsarkar, Dwarkanath & Pant (1977, 1978) in which data on fructose and citric acid concentration in electro-ejaculated semen of Magra rams, obtained during the winter and spring, have been presented. A need was felt for understanding the pattern of concentration of these constituents throughout the year in semen collected from rams under natural conditions. The present investigation was, therefore, undertaken to study the seasonal pattern of concentration of two important chemical constituents (fructose and citric acid) and physical (ejaculate volume and sperm concentration) characteristics of the naturally ejaculated semen of two important Indian desert sheep breeds, the Marwari and the Magra. A similar, though short-term, study on the semen of an exotic breed, the Corriedale, was also undertaken.