The stability of unidirectional, equally spaced fibers in the plane of a composite plate is formulated by treating the fibers as beams and the matrix by the theory of generalized plane stress. Critical values of the axial load and the corresponding buckling modes are evaluated numer ically and shown graphically for various values of the parameters. Approximations leading to explicit expressions for the critical values are introduced, and restrictions on the applicability of the approximate results are determined. Experimental evidence of the occurrence of buckling modes of the type considered is presented.