  The ``six degrees of separation" between any two individuals on Earth has
become emblematic of the 'small world' theme, even though the information
conveyed via a chain of human encounters decays very rapidly with increasing
chain length, and diffusion of information via this process may be very
inefficient in large human organizations. The information flow on a
communication network in a large organization, the University of Oslo, has been
studied by analyzing e-mail records. The records allow for quantification of
communication intensity across organizational levels and between organizational
units (referred to as ``modules"). We find that the number of e-mails messages
within modules scales with module size to the power of $1.29\pm .06$, and the
frequency of communication between individuals decays exponentially with the
number of links required upwards in the organizational hierarchy before they
are connected. Our data also indicates that the number of messages sent by
administrative units is proportional to the number of individuals at lower
levels in the administrative hierarchy, and the ``divergence of information"
within modules is associated with this linear relationship. The observed
scaling is consistent with a hierarchical system in which individuals far apart
in the organization interact little with each other and receive a
disproportionate number of messages from higher levels in the administrative
hierarchy.
