Using fluorescence lifetime (tau(t)) data reported in previous papers, radiative and nonradiative rate constants were estimated for anthracene (A) and 9-methylanthracene (MEA) in methylcylohexane at 25 degrees C and pressures up to 700 MPa. The estimation was also made for MEA at pressures up to 400 MPa at 15-55 degrees C. The pressure and temperature dependences of the nonradiative rate constant are discussed from the viewpoint of the medium effect on the S-1-T-2 intersystem crossing (ISC) process, taking account of the vibrational-level dependence of ISC rate constant.