We have used high resolution two-dimensional gel electrophoresis to identify and characterize proteins that may represent products of genes involved in establishing positional information along the proximal-distal axis of the regenerating forelimb of the newt Notophthalmus viridescens. At least 24 proteins have been found whose synthesis and (or) abundance is increased in proximal (midstylopodial) regenerates relative to midzeugopodial (distal) regenerates at either of two regeneration stages, the early dedifferentiation and moderate bud stages. Four of these same proteins show an axial asymmetry at both stages. Ten distal-specific proteins were also identified, although only one was common to both stages. More significantly, 6 of these 34 proteins (molecular masses of 73, 73, 51.5, 44.0, 19.5, and 16.5 kilodaltons and isoelectric points of 6.70, 6.74, 6.0, 6.05, 5.9, and 6.98, respectively) are regulated to proximal levels by treatment of distal regenerates with retinoic acid (RA) at both stages. An additional five are proximalized by RA at only one regeneration stage. Since the effect of RA is to proximalize positional information in blastema cells, these 11 proteins represent gene products that could be involved in a biochemical cascade leading to the establishment of positional information in the regenerating limb along this axis.