Abstract: In the last year G. Caristi and M. Stoka [2] have considered Laplace type problem for different lattice with or without obstacles and compute the associated probabilities by considering bodies test not-uniformly distributed. We consider a lattice with fundamental cell a parallelepiped in the Ecuclidean Space E<sub>3</sub>. We compute the probability that a random segment of constant length, with exponential distribution, intersects a side of the lattice.