Base hydrolysis and acidification of a polyimide film resulted in a surface that resembles the poly(amic acid), which is the polyimide precursor. This modification was thoroughly characterized and found to offer an unusual opportunity to control the depth of modification. The modified surface was used as a substrate for subsequent organic reactions, including conversion of the surface to isoimide by reaction with trifluoroacetic anhydride in pyridine. The isoimidized surface was isomerized back to polyimide by heating. The reduction of the polyamic acid surface was also accomplished, resulting predominantly in a surface in which all carbonyls were reacted to give alcohol and amine functional groups. All surfaces were characterized by contact angle, XPS, and FTIR measurements and by comparison to the reaction products obtained using model compounds. © 1992, American Chemical Society. All rights reserved.