AIM: The manual files are still widely used for initial canal negotiation prior the use of nickel-titanium shaping instruments, to determine working length and to verify patency. A mechanical glide path can be performed using manual files with handpieces, such as M4 Handpiece (SybronEndo, USA) that allows a 30°/30° reciprocating motion. The Pathfinders (SybronEndo, USA) are hand files designed to negotiate complex canals, made from stainless steel (SS) or carbon steel (CS) alloys. The aim of this in vitro study was to compare cyclic fatigue resistance of these two different types of manual Pathfinder instruments used in a M4 reciprocating handpiece in double curved artificial canals. MATERIALS AND METHODS: Manual instruments designed for glide path (size #9 ISO .02 taper) made from different alloys were selected: Group SS -stainless steel Pathfinders (Sybron Endo) and Group CS - carbon steel Pathfinders size K2 (Sybron Endo). Ten instruments of each group were tested for resistance to cyclic fatigue with a reciprocating M4 handpiece inside an artificial S-shaped canal; the time to fracture was recorded for each file and data were statistically analyzed (ANOVA). RESULTS: Mean values (and SD) were 527 (± 89) seconds for the CS instruments and 548 (± 104) seconds for the SS files. No significant differences were observed between groups (p=0,062). CONCLUSIONS: According to the results, both carbon and stainless steel instruments presented similar fatigue resistance when used with M4 reciprocating handpiece in double curved canals.