Two new capacitor microphones, the Sennheiser type MKH 404 and the Akustische und Kino Gerate type 628, have been produced which employ transistor circuits and radio-frequency polarizing of the capsule; both have a cardioid directional characteristic and are of the end-fire type. Measurements of the frequency characteristics have been carried out for sound incident at various angles; the degree of self-generated noise and interference from wind and magnetic fields have also been determined. The frequency characteristics of the Sennheiser type MHK 404 microphone vary more than usual with angle of sound incidence but the level of internally generated noise is extremely low. The axial response of the AKG type 628 microphone extends to about 15 kHz (kc/s) but the back suppression is poor between 3 kHz and 8 kHz; on the other hand, the self-generated noise level is the lowest so far met with in a capacitor type microphone. The specimen tested was a pre-production model; the production version will be coded C600, C601 or C602 according to the power supply arrangements.