A study of serum antibodies raised against morphine (57272) in 35 workers occupationally exposed to opiates at a narcotics manufacturing facility was conducted. Blood sera were collected before and 10 months after an improved respiratory protection program was implemented at the facility and assayed for specific immunoglobulin-G (IgG) antibodies raised morphine using a radioimmunoassay. Inhibition studies using morphine and morphine derivatives utilizing an enzyme linked immunosorbent assay were also performed. At the second sampling, serum samples were six persons employed at the facility in clerical or administrative positions, 18 drug abusers being treated for heroin use, seven burn patients who used morphine sporadically for pain, and three persons in a drug treatment program who were drug free were also analyzed. Serum IgG antimorphine antibody concentrations in the exposed workers before and after implementation of the respiratory protection program were 4.48 and 1.19, expressed as absorbance units (Au), respectively. The decrease was statistically significant. Serum IgG antibody concentrations in the unexposed workers averaged 1.61Au. The antibodies were specifically directed against morphine, although some cross reactivity with the other morphine derivatives was observed. Preliminary results from the subjects in the drug abuse treatment program indicated that serum IgG antimorphine antibody concentrations were significantly elevated. The authors conclude that serum antimorphine antibody concentrations are elevated in persons occupationally exposed to opiate dusts. Elevated concentrations of these antibodies are also found in heroin abusers.