Differences between mean monthly winds obtained from actual observations and geostrophic wind derived from mean monthly altitudes of constant-pressure surfaces are examined for January and July at four levels between 10,000 and 40,000 ft. Differences in speed for both east-west and north-south components are significantly and unexpectedly large. These results demonstrate the advantage of using observed winds rather than deduced values to provide climatic winds at altitudes betweet 10,000 and 40,000 ft. Modification of the existing system to include winds from actual observations wherever and whenever possible is recommended. (Author).