Low-cost point-to-point radio systems are available at a number of frequencies in both the centimetre and millimetre wavebands for local business applications. In urban areas a high degree of cochannel operation is predicted, both for reasons of spectral efficiency, and because forecast demands greatly exceed the number of available channels. The paper presents an initial probabilistic study of the limiting cochannel interference effects, based on an idealized flat circular locality model. The study indicates that high system populations, or area capacities, should be achievable. For example in a typical large metropolitan area, the predicted capacities for one way systems sharing a single channel, are several hundred for centimetre wave (13 GHz) systems, and several thousand for millimetre wave (39 GHz) systems. It is demonstrated furthermore that the area capacity is proportional to the square of the antenna diameter to wavelength ratio. There is thus a high incentive to employ equipment with relatively large antennas, and to operate wherever possible in the millimetre wavebands.