This report deals with the reconstruction of the distribution of membrane thickness T from that of orthogonal intercept length L₀, measured in random section planes. In such planes the membrane appears as a band and the linear distance from one of its boundaries perpendicular to the opposite one is the length of the orthogonal intercept. Using a membrane model, an integral equation relating the probability density functions of orthogonal intercept length f(l₀) and membrane thickness g(τ) is derived. Relations between moments are derived and the analytic solution to the problem of reconstructing g(τ) from f(l₀) is given. The parametric approach by which it is assumed that g(τ) has some known analytic form with unknown parameters is considered, and the use of a suggested analytic form for describing the thickness distribution of the human glomerular basement membrane is discussed.