Aqueous polypyrrole latex reacted at room temperature with good nucleophiles such as thiols and amines, while alcohols showed no reaction. The reactions were followed by visible, XPS, and ESR spectroscopy, radiolabeling, and conductometric titration. This finding provides fora facile method for the modification of polypyrrole surface chemistry. A mechanism of chemical addition into the conjugated polymer chain is proposed which is consistent with these results.