The formation and the equilibrium configurations of dislocation multipoles on two slip planes are considered theoretically in detail. It is found that the predicted arrays, assuming a trapping formation mechanism, are in fair agreement with those observed in Cu 10 % at. Al alloys deformed into stage I of the work-hardening curve. The calculations show that if two Frank-Read sources on parallel slip planes emit dislocation loops, the dislocations will form a multipole spontaneously in the absence of any effective applied stress. If the two sources lie a distance l apart on slip planes separated by y, the maximum number of dislocations which each source can emit varies between 2 l/7 y (when the line joining the sources is perpendicular to the Burgers vector, b) and 116 y (when the line is parallel to b). The stress required to decompose a multipole, once formed, is found to be almost independent of n, the number of dipoles in the multipole, and is given to a good approximation by : τp = Gb/2 πkγ where k = 2 and 4(1 - v) for screw and edge dislocations respectively. A theory of stage I work-hardening based on the above calculations yields a relationship between stress (τa - τF) and strain (ε) of the form : ε = q [(τa- τF)/G]3 where q depends on the density and distribution of active Frank-Read sources. If a random distribution of sources, whose average separation projected into a plane normal to the slip plane is ∼ 10µ is assumed, good agreement is obtained between theory and the experimental stress-strain curve of magnesium measured by Hirsch and Lally (1965)