In a photographic diffusion transfer system a hydroquinone silver halide developing agent, containing a methyl, ethyl or alkoxy group in the 5 position and a carboxyalkyl group containing 4 to 9 carbon atoms in the 2 position of the hydroquinone nucleus, provides reduced stain as well as improved maximum density, desired black tone, without loss of other desired sensitometric properties. Such developing agents, e.g. 6(2,5-dihydroxytolyl) hexanoic acid, are especially useful in a black and white silver salt diffusion transfer process. They can be incorporated in a photographic element and can be employed in combination with other silver halide developing agents.