YES!!! I have done this for a while now... I have found that in varying amounts of MH/HPS througout the entire life cycle, I have produced bigger yields, consistantly, as compared to the "old" method of MH for veg, and HPS for flower... I use more MH than HPS during seedling/veg stages, and then gradually increase the HPS as I begin flowering, still keeping AT LEAST a 250 or 400W MH in there with all my HPS's... I absolutely stand behind this method, and suggest it to everyone... That with proper ventilation, temp control, CO2, and great, all-natural, organic nutes, makes for the dankest colas and nuggets I've ever seen, from the West Coast to the East Coast...and everywhere in between... The MH is purported to increase the odds of females turning up, but I dunno for sure on that one, although I usually have better than the "textbook" 50/50 results with females, but the presence of MH during flowering also increases the resin production via trich production, because it is the plant's natural response to UV spectrums, which are present in MH light... And it also seems to help keep internodal spacing closer, providing fo chunkier, fatter colas... So, absolutely go with both... I even have mine timed to mimic nature, in that my HPS's will come on first, like sunrise, and then three hours into the 12 hour on period, my MH comes on for six hours, and then goes off, just like sunset... SO, why wouldn't anyone want to better re-create nature in the lighting of their gardens?