  We carried out photometric and low-resolution spectral observations of six
eclipsing ultrashort-period binaries with MS components. The light curve
solutions of the Rozhen observations show that all targets are overcontact
systems. We found well-defined empirical relation "period -- semi-major axis"
for the short-period binaries and used it for estimation of the global
parameters of the targets. Our results revealed that NSVS 925605 is quite
interesting target: (a) it is one of a few contact binaries with M components;
(b) it exhibits high activity (emission in H$\alpha$ line, X-ray emission,
large cool spots, non-Planck energy distribution); (c) its components differ in
temperature by 700 K. All appearances of high magnetic activity and huge
fillout factor (0.7) of NSVS 925605 might be assumed as a precursor of the
predicted merging of close magnetic binaries. Another unusual binary is NSVS
2700153 which reveals considerable long-term variability.
