A mathematical technique was developed to calculate a log-normal distribution for sample results. This is then compared with a Limiting distribution defined by the sampling time, the Time-Weighted Average and the Ceiling Limit standard for the material tested. The technique provides a more effective means to decide if either or both the T.W.A. or Ceiling Limit has been exceeded. Sample times from 10 minutes to 4 hours are considered. A similar technique has previously been reported for evaluating benzene exposures. Examples are provided to illustrate the procedure.