The biological effect of Coffea cruda 30c was investigated in rats pre and post treated with caffeine. The experimental subjects were male Wistar rats. Caffeine was administered intraperitoneally at the beginning of a sleep period. Coffea cruda 30c (0.1 ml) was administered orally, a contemporaneous control group was tested. The Electroencephalogram (EEG) was recorded in the parietal region during the following sleep cycle. The effect was evaluated by three EEG parameters: the spectral power in delta (0.5-2.5 Hz) and slow 0.32-0.48 Hz bands and the slow/delta power ratio. These markers were analyzed vs time for control and homeopathic groups, blind. In the pretreated set, a similar pattern was identified for control and verum groups up to the 4th hour. From the 5th hour on, power in the delta band was statistically higher in the verum. Spectral power in the slow band and power ratio for the verum group was smaller than the control group from the 6th hour on. In the post-treated set, two verum sub-groups were identified: Post v-A: did not exhibit significant differences from control; Post v-B: displayed an opposite tendency than pre-treatment verum. We conclude that Coffea cruda 30c modifies sleep pattern increasing sleep intensity with pre-treatment. In a subset of the post-treated animals Coffea 30c appeared to reinforce the effects of caffeine.