A truncated variant of TPK1, the yeast cAMP-dependent protein kinase catalytic subunit, was overexpressed in an engineered strain of Saccharomyces cerevisiae, purified by liquid chromatography, and crystallized from solutions of 2-propanol and magnesium at alkaline pH. The crystals are hexagonal dipyramids, space group P6(1)22 (P6(5)22), with unit-cell parameters a = b = 61 angstrom, c = 320 angstrom. Large single crystals suitable for diffraction analysis are obtainable by microseeding, and diffract beyond 2.8-angstrom resolution. Crystal density measurements reveal 12 kinase monomers per unit cell with a single kinase monomer per asymmetric unit.