Polyamide reverse osmosis membranes, used successfully for water desalination, are made from the interfacial reaction of meta-phenylenediamine (MPD) with trimesoyl chloride. One problem with the membrane is that its performance is deteriorated upon prolonged exposure to chlorine often used for disinfecting feedwater. ATR-FTIR and XPS analysis show chlorine reacts with the amide hydrogen and is attached to the polyamide membrane. A chlorine resistant membrane has been made using a non-MPD amine and appears to be five times as chlorine-resistant as the MPD-based membrane. ATR-FTIR and XPS analysis also show the chlorine-resistant membrane picks up chlorine much less than the MPD-based membrane upon exposure to chlorine. Monochloramine does not appear to adversely affect polyamide membranes. Includes 10 references, table, figures.