A recombinant form of Klebsiella pneumoniae maltohexaose-producing alpha-amylase has been overexpressed in Escherichia coli and purified to homogeneity. Crystals were obtained at 293 K by the microbatch technique using 80 mM sodium/potassium phosphate buffer pH 6.2 containing 8% polyethylene glycol 3000, 4% polyethylene glycol 3350 and 40 mM sodium thiocyanate. Crystals of the overexpressed recombinant enzyme diffracted to better than 2.5 A resolution at 95 K using a synchrotron-radiation source. The crystals belong to the primitive monoclinic space group P2(1), with unit-cell parameters a = 74.8, b = 107.6, c = 82.2 A, beta = 96.2 degrees. Assuming the presence of two molecules per asymmetric unit, the V(M) value for the crystal was 2.3 A(3) Da(-1), indicating a solvent content of 47%.