Antibody to the antibiotic chloramphenicol was obtained by immunizing rabbits with a chloramphenicol derivative coupled to bovine gamma globulin. Production of antibody was demonstrated by the precipitin and complement fixation reactions with "reduced chloramphenicol" coupled to rabbit serum albumin as the test antigen. Specificity of the antibody was confirmed in that crystalline chloramphenicol completely inhibited complement fixation and precipitin reactions. "Reduced chloramphenicol" coupled to human serum albumin provides an antigen for the detection of antibody to chloramphenicol, if it occurs in human serum in dyscrasias. With quantitative complement fixation, as little as 10 -5 μg (4 × 10 -14 mole) of chloramphenicol was detectable by the inhibition assay.