The advent of high-frequency transistors has created a need for improved oscillographs. Present instruments are neither fast enough nor sufficiently sensitive to display the low-amplitude high-impedance waveforms generated by these high-frequency transistors. A transistor oscillograph using the sampling principle has therefore been designed having a response extending from d.c. to 300 Mc/s, corresponding to a rise time of about 1.5 millimicrosec, and a sensitivity which gives a full-scale deflection for an input of a few hundred millivolts; the input impedance is equal to 1 pF and 1 megohm parallel. With one exception, all the transistors employed have α cut-off frequencies in the region of 10 Mc/s.A basic oscillograph using a total of ten transistors is described the first part of the paper, followed by a more sophisticated version with improved linearity and double-beam display.