We present simultaneous high time resolution ( 1-10 Hz ) X-ray and optical observations of the persistent LMXBs Sco X-1 and V801 Ara ( =4U 1636-536 ) .
In the case of Sco X-1 we find that the Bowen/HeII emission lags the X-ray light-curves with a light travel time of \sim 11 - 16 s which is consistent with reprocessing in the donor star .
We also present the detection of three correlated X-ray/optical bursts in V801 ara .
Although this latter project is still in progress our preliminary results obtained by subtracting the Continuum light-curve from the Bowen/HeII data provide evidence of orbital phase dependent echoes from the companion star .