Following previous light and ultrastructural cytochemical reports, this paper presents the first zymograms of Kurloff cell acid phosphatases extracted from highly purified cell suspensions. Using isoelectric focusing, up to 20 isoenzymes were observed both with hexazotised pararosanilin or fast garnet GBC as coupler and naphthol ASB1 phosphate as substrate. Most were tartrate-labile. After Clostridium-derived neuraminidase digestion, the highly stained bands observed at pH 4-5 disappeared and, simultaneously, a few alkaline bands were enhanced. Two main bands of Mr 190,000 and 500,000 were characterized by their acid phosphatase activity after electrophoresis on a 4-15% gradient native polyacrylamide gel.