In order to examine the effect of metal salts on the blood level of chloramphenicol, oral administration of chloramphenicol solution, containing ferrous lactate, calcium lactate, magnesium oxide, or synthetic aluminium silicate, was made in rabbits and blood level of chloramphenicol was measured. In all of these cases, there was retardation of the time required until highest blood level is reached or clear indication of maximum blood level, compared to administration of chloramphenicol alone. Combined use of sodium ethylenediaminetetraacetate or sodium metaphosphate in this case showed the same blood level as that of chloramphenicol alone. Factors influencing blood level might also include crystal size, chloramphenicol crystals of various size were administered similarly. Measurement of blood level indicated that administration of fine crystals resulted in the highest blood level one hour after administration and this time required to reach the highest level lessened gradually as the crystal size became larger. However, there was no difference in the amount of total nitro compound excreted into the urine according to crystal size and this probably suggests that there is no difference in the absorption of chloramphenicol according to its crystal size.