Muskrat (Ondatra zibethicus rivalicius) movement and activity patterns were studied in a Louisiana coastal marsh. Trap success was 8.2% in January-February, but only 3.3% in June-August. Of 46 muskrats captured, 65.2% were males. Lodge use was greater than expected in JanuaryMarch and less than expected in April, July and August (X2 =92.5, N =557, P < 0.01). No radio-collared muskrats (11 males and 6 females) were observed rearing young. Five (33.3%) muskrats emigrated in the spring and 3 of the dispersals occurred during a storm tide (29 March- 3 April). Long movements (>70 m) within the study area were associated with high water levels (>20 em). Average home range (0.7 ha, SE = 0.2, N = 44) and hourly movements (33.8 m, SE = 1.8, N = 695) recorded on diel tracking sessions varied widely among individuals.