Benzothiazole side chains featured in zopolrestat (1a) and its congeners were incorporated into oxophthalazineacetic acid replacements, including indazole, pyridazinone, and pyridopyridazinone with a pendant acetic acid moiety. Potent aldose reductase inhibition activity among resulting compounds is as widespread as it is in the earlier zopolrestat series, thus lending further support to our hypothesis that there is a binding site on the aldose reductase enzyme with strong affinity for benzothiazoles. Representative new compounds 1-[(5,7-difluoro-2-benzothiazolyl)-methyl]-1H-indazoleacetic acid (62), [6-[[5-(trifluoromethyl)benzothiazol-2-yl]methyl]-8-oxo- 6H-pyrido[2,3-d]-pyridazin-5-yl]acetic acid (70), 3,4-dihydro-4-oxo-5,6-dimethyl-3-[(5,7-difluorobenzothiazol-2-yl) methyl]-1-pyridazineacetic acid (79), and 3,4-dihydro-4-oxo-5,6-cyclohexano-3-[[5-(trifluoromethyl) benzothiazol-2-yl]-methyl]-1-pyridazineacetic acid (82) are potent aldose reductase inhibitors with IC50s of 30, 2.1, 5, and 52.2 nM, respectively. The best of these compounds, 79 and 82, also inhibit accumulation of sorbitol in rat sciatic nerve in a model of diabetic complications, when administered orally at 10 mg/kg. The inhibition values are 76 and 61%, respectively. In addition to benzothiazole, we have examined its surrogates effective in potentiating aldose reductase inhibition activity, including benzoxazole and aryl[1,2,4]oxadiazole. Structure-activity relationships emerging from this program are also discussed.