A method of operating a drivetrain of a motor vehicle which comprises a hybrid drive with a combustion engine coupled by a clutch to an electric motor. To start the combustion engine with the electric motor, the clutch is partially engaged to a slipping condition to deliver electric motor torque from a starting value, the torque transmitted by the clutch is increased to a first final value. If during this, the combustion engine begins turning, the break-away torque of the internal combustion engine is determined. If the combustion engine does not begin turning, the clutch is further engaged to a slipping condition starting from a second initial value, such that torque transmitted by the clutch increases linearly until the combustion engine begins turning, and the break-away torque of the internal combustion engine is determined from the clutch torque at which the combustion engine begins turning.