  ABSRACT: We review recent progress on testing the hypothesis of the existence
of cosmic string perturbations in microwave background maps. Using an
analytical model for the string network we show that the predicted amplitude
and spectrum of MBR fluctuations are consistent with the COBE data for a
reasonable value of the single free parameter of the string model (the mass per
unit length of the string $\mu$). To {\it distinguish} the predictions of
cosmic strings from those of Gaussian models it is necessary to apply specific
{\it statistical tests} which are sensitive to non-random phases of the MBR
temperature maps. We discuss two such statistical tests: First, the probability
distribution and the moments of fluctuations ${{\delta T}\over T}$ and second
the corresponding statistical quantities for the {\it gradient} of fluctuations
along a fixed direction. We show that the second statistic can detect cosmic
string specific signatures on MBR temperature maps with resolution of a few
arcminutes or smaller.
