Plasmodia of the myxomyceteBadhamia utricularis were allowed to incorporate colloidal gold particles for varying periods of time. After fixation and sectioning they were examined by transmission electron microscopy to evaluate the intracellular position of the uptake marker. Some sections were treated with phosphotungstic acid-chromic acid which stained the plasma membrane, as well as vesicular, secondary lysosomal, and autolysosomal membranes. Some plasmodia that had taken up gold particles were injured, and sections of the resulting cytoplasmic droplets were examined to determine the involvement of various membrane bound compartments in the process of plasma membrane regeneration. Endocytotic vesicles and secondary lysosomes were found to be the major identifiable contributors to the new plasma membrane, which was stained by the phosphotungstic acid-chromic acid procedure. The internal vacuolar spaces of cytoplasmic droplets were shown to be bounded by phosphotungstic acid-chromic acid positive membranes that appeared to be formed in the same manner as the new plasma membrane.