Earlier studies of OPA anhydrolase from the squid, Loligo pealei, report that the enzyme has a molecular weight near 26 kDa, despite the common observation that SDS-PAGE experiments do not support this conclusion. Recent results from protein sequencing and cloning experiments now suggest that the enzyme found in squid hepatopancreas has a molecular weight of about 42 kDa. The enzyme easily degrades into two fragments of 16 kDa and approximately 26 kDa. N-terminal sequence analyses of the intact enzyme and the 16 kDa fragment blotted from an SDS gel and sequenced from the blot have shown conclusively that the intact 42 kDa protein has a blocked N-terminus. Sequence data obtained previously are from the N-terminal portion of the 16 kDa fragment. Additional support for this interpretation has been obtained from PCR analysis of L. pealei mRNA and cDNA. The partial (30 residue) sequence presented here reveals no indication of similarity to any other OPA anhydrolase or aryldialkylphosphatase (EC 3.1.8.1.).