Abstract: The adjacency effect in photographic development was studied. The p-phenylene-diamine type developers were used in both black-and-white and color development for the convenience of comparison. In black-and-white development a linear relationship was found to hold between the density increment on the boarder side (δ) and the large-area density difference (H) for a given film-developer combination:δ = αH + b a can be used as a measure of the magnitude of the adjacency effect. The influences of developer activity, concentration of developing agent, developing time and pH of the developer on the adjacency effect were also studied. In color development a complicated relationship between the adjacency effects of silver and dye images was observed.