Several positions in the southern spiral arm and the interarm disk of NGC 4321 have been observed in CO (J = 1 to 0) using the NRO 45 m telescope at Nobeyama, Japan. The analysis shows evidence for streaming motions in the arms, together with an exponential radial decrease of both the integrated CO emission and the velocity width at the observed positions, with comparable scale lengths. The arm/interarm contrast ratio of CO integrated emission shows values ranging from less than one to four.