Asymmetry is a common trait in spiral galaxies and is particularly frequent among Magellanic spirals . To explore how morphological and kinematic asymmetry are affected by companion galaxies , we analyze neutral hydrogen observations of the interacting Magellanic spirals NGC 4618 and 4625 . The analysis of the H I distribution revealed that about 10 % of the total H I mass of NGC 4618 resides in a looping tidal structure that appears to wrap all the way around the galaxy . Through calculations based on derived H I profiles , we show that NGC 4618 and 4625 are no more asymmetric than non-interacting Magellanic spirals analyzed by Wilcots & Prescott ( 2004 ) . We also derive rotation curves for the approaching and receding sides of each galaxy . By fitting the mean curves with an isothermal halo model , we calculate dynamical masses of 4.7 \times 10 ^ { 9 } M _ { \odot } and 9.8 \times 10 ^ { 9 } M _ { \odot } out to 6.7 kpc , for NGC 4618 and 4625 respectively . While the rotation curves had systematically higher velocities on the receding side of each galaxy , the effect was no more pronounced than in studies of non-interacting spirals ( Swaters et . al . 1999 ) . The degree of interaction-driven asymmetry in both galaxies is indistinguishable from the intrinsic degree of asymmetry of lopsided galaxies .