The dual gold + mercury (Au + Hg) amalgam electrode was found to be an effective detector for S-sulfocysteine (SSC). Using flow injection analysis, a 20 pmol mass detection limit was achieved using a 20 mu l injection volume. Cystine and SSC were shown to behave quite differently in this detection system. The signal from cystine displayed a dependence on flow rate reflective of simple mass transfer, while the signal from SSC was more sensitive to mobile phase flow rate. The cystine signal was insensitive to pH, while SSC’s signal depended significantly on pH. The SSC reduction reaction at the upstream Au + Hg electrode was determined by cyclic voltammetry to be RSSO3- + 2H(+) + 2e(-) --> RSH + HSO3-. The signal monitored at the downstream electrode was attributed mainly to the oxidation of Hg to Hg cysteinate below pH4. Both cysteine and bisulfite contributed to the detection signal above pH 4.5. The optimum pH for the detection of SSC was approximately 5.2.