An amino-derivative of parathion was prepared and conjugated to human serum albumin (HSA) and bovine thyroglobulin (BTG) via diazonium condensation. Spleen cells producing high titer antibody were removed and fused with myeloma cells of SP2/0 origin. Using a conventional immunization protocol, we generated nine stable murine monoclonal antibodies (MAbs) producing cell lines to parathion. After four successive limiting dilutions, antibodies produced by nine clones had high affinities, ranging from 10(9) to 10(12) M(-1). These clones were found to be of IgG class and IgM class with k light chain. Subclass determination showed that the clones produced IgG(1), IgG(2a), IgG(2b), and IgM types of antibody. One clone (2H(9)) was used to establish the calibration curve with a sensitivity of 26 ng/mL, a practical working range of 46.8-6000 ng/mL parathion.