AFMPB: an adaptive fast multipole Poisson-Boltzmann solver for calculating electrostatics in biomolecular systems. It is described an adaptive fast multipole Poisson-Boltzmann solver for computing the electrostatics in biomolecules. This solver combines the fast multipole method with the Krylov subspace methods, which are applied to solve a well-conditioned boundary integral equation of the linearized Poisson-Boltzmann equation. Numerical experiments show the efficiency of the method in the framework of relatively large molecules on current desktop computers.