The effect of different types of dietary fat on muscular acetylcholinesterase (Ache) activity was studied in rats. Enzyme activity was determined in two leg muscles: red soleus and white gastrocnemius. After one week of feeding with fat free diet (20% of energy from protein with casein as its source and 80% of starch as carbohydrate) rats were fed one of four isocaloric diets (16 kJ/g; 20% protein, 60% carbohydrate and 20% fat) differing in source of dietary fat (sunflower oil - S group; lard - L; palm oil - P; rapeseed oil - R). There were no significant differences in Ache activity in soleus and gastrocnemius after fat free regimen. Diet intake containing fat during the first week evoked decrease in Ache activity in group L in soleus and in groups S, L and R in gastrocnemius. Palm oil diet feeding did not change Ache activity as compared to that observed after fat free diet. After subsequent two weeks of supplying diets containing fats Ache activity increased in soleus in all dietary groups; in gastrocnemius it increased in groups S and L. Thus, after three weeks of consuming fats from different sources in both muscles significant differences in Ache activity among various dietary groups were not observed; its activity in soleus did not differ significantly from that observed after fat free diet in all groups, in gastrocnemius it remained significantly lower only in R group. These results suggest that the influence of dietary fat on muscular Ache activity could be a transient phenomenon and depends on muscle type. However, taken into consideration different dependence of Ache muscular isoforms on factors regulating, adaptations based on changes in their relative participation in overall Ache activity could not be excluded.