Field emission microscopy studies of carbon nanotubes grown by the pyrolysis of ferrocene on a tungsten field emitter are reported. A field emission current density of 1.5 A cm(-2) has been drawn from such an emitter at a field of 290 V/mum, and this density is considerably higher than that found with planar cathodes. Accordingly, the field enhancement factor, calculated from the slope of the F-N plot in the low field region is also large. Field emission micrographs reveal the lobe structure symmetries typical of carbon nanotube bundles. The emission current is found to be remarkably stable over an operating period of more than 3 h for current values of up to 500 muA.