Hinted by a symbiotic relationship between rumen microorganisms and host ruminant in utilization of inorganic sulfur compounds such as sodium sulfate and ammonium sulfate, an investigation was conducted to determine a similar symbiotic effect between ceacum microflora and host rabbit, for ammonium sulfate. Radioactivity of fecal emission was detected from the first day of administration but the radioactive compound(s) was not precipitated by barium chloride. A similar fact was found when the labelled sulfate-sulfur was administered by intraperitoneal injection. When urinary ejection was fractionated into 3 parts, namely, trichloroacetic acid precipitate, barium chloride precipitate and supernatant fractions, radioactivity was almost equally distributed into barium chloride precipitable and supernatant fractions with a minor beta-ray emission from TCA precipitated fraction. Radioactivity was detected in hairs of experimental subjects regardless the mode of drug administration. Our finding shows that angola rabbit possesses per se the capacity of such utilization independent to its ceacum microflora. Liver homogenates made 48 hours after the suspension of drug administrations showed no radioactive emission from its barium chloride precipitated fracton. Majorities of beta-ray emission was detected in the TCA precipitated fraction. A minor amount of count, detected from supernatant is interpreted as an evidence that in the liver, transformation of inorganic sulfate sulfur into other sulfur compound (s) is a pre-requisite for protein incorporation or other physiological or metabolic process. The results of in vitro test for microbial incorporation of labelled sulfate-sulfur show that when ceacum microfiora are incubated under anaerobic conditions the microorganisms can incorporate the labelled element into their cellular protein. The capacity of doing so seems to be increased by a prolonged exposure to or contact with such compound expressed otherwise, they can be trained to do so.