A method for studying deuterium-deuterium fusion neutron production in condensed matter together with experimental results are presented. The method is based on long-term measurements for comparison among different cells with electrolytically charged palladium cylinders and background. The statistical method used for data reduction is presented, which enables identification of even very small effects. In the experiment, for an ∼100-h period an excess counting rate of ∼3 count/h (averaged for this period) above the background level was found.