Abstract: According to the analysis on light chain pattern of single fibers,ther were one third of fibers in rat soleus muscle which had a distinct staining band at the position of LC3,while the remaining fibers did not show such band by present method due to its minute quantity.No matter whether of not LC3 appeared,the electrophoretic patterns of fiber proteins between Sol and EDL were completely different,including the differences of molecular weights of LC1,LC2 and the distance travelled along the gel between LC1 and tropomyosin of fibers of the two muscles.Experiments have been performed to see if LC3 exists in each fiber of soleus muscle.We deduced it by analyzing randomly three fibers in one electrophoretic gel to show the chance of appearance of LC3 by simple probability calculation and a great exceed (89%) over the "theoretical" value (67%) in probability was achieved.For the same purpose,we also analyzed guinea pig soleus which was known to have pure slow fibers,and conform to that,100% of fibers tested contained LC3;and finally 56% of cat soleus fibers was found to contain LC3 whose appearnce were clearly related to their intensity of protein staining on electrophoretic gels.Attempts have also been made to explore the corelation between light chain characteristics and ATPase activity of fibers.Preliminary results indicated that there were no such parallel relationship.