A 1-methylcarbapenem compound ethanolate of the formula (I-1) in the crystalline form that shows main peaks at interplanar spacings d=7.60, 6.69, 6.33, 6.14, 5.15, 4.58 and 4.48 in the X-ray powder diffraction pattern obtained with Cu K.sub..alpha. irradiation ##STR00001## and a 1-methylcarbapenem compound tetrahydrate of the formula (I-2) in the crystalline form that shows main peaks at interplanar spacings d=11.68, 8.79, 7.53, 6.57, 5.58, 5.37, 3.99 and 3.09 in the X-ray powder diffraction pattern obtained with Cu K.sub..alpha. irradiation ##STR00002## These compounds are useful for treating or preventing bacterial infections.