According to the recommendations of the German MAK list, inhalable dust (or so-called ‘total dust’) is currently sampled using probes having intake air velocities of 1.25 m s −1 . Annular slot probes conforming to this requirement were developed for sampling independently of wind direction. Probes with a specific intake direction may also be used for sampling in well-defined air flows, provided the plane of the sampler entry is placed at 45° to the flow direction. Systematic studies of the sampling efficiency of such probes did not, however, show a consistent correlation with human inhalation efficiency (determined by experiments with model human heads in wind tunnels); instead, they showed that sampling efficiency is dependent also on the detailed geometric design of the probes. Better results have been obtained with so-called blunt probes, although development in this field is not yet concluded.