Development of germ tubes from conidia on the needle surface and in the stomatal antechamber of Scotch pine [Pinus sylvestris] was studied by scanning electron microscopy. Germ tubes usually grew appressed to the needle surface and followed contours of the epidermis. Often germ tube growth seemed to be directed specifically toward an individual stoma. In the antechamber the germ tube usually increased in diameter, became thick-walled, melanized, rugose in surface texture and irregular in general form and outline. It grew in a meandering fashion without branching, or it branched and developed a convoluted form. Penetration between the guard cells and subsequent growth in the substomatal chamber or mesophyll could follow either type of growth in the antechamber but did not always occur. Germ tube behavior patterns may be the result of responses to stimuli emanating from individual stoma.