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An electron microscope study of three niobium specimens of different, moderate purities (99.7 to 99.93%) leads to the revelation of three interactions between two perfect, glissile dislocations in the {110} <111> slip systems. All interactions produce sessile dislocations with b = a<100> or a<110>. Despite the nonslip character of the product dislocations, one interaction, (4), actually assists the slip process by promoting cross slip of the mobile reactant dislocation. Interaction (5) is energetically prohibited in equilibrium conditions. Its occurrence is probably made possible under stresses in nonequilibrium conditions so as to accomodate another interaction of type (3) occurring on the opposite side of the same reactant dislocation in loop form. The present results thus imply that the number of interactions among glissile dislocations in the {110} planes is more than 16 for the body‐centered cubic metals. Also, it is concluded that even if the product dislocations are sessile in nature, not necessarily all of the interactions would hamper the slip process as has been suggested by previous workers.

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