To follow on from the two previous posts, you don't give enough information to help us offer any useful advice, other than to recommend that you take your dog to see the vet as soon as possible, if not today. This applies especially if he's been vomiting for more than 24 hours.
From time to time, dogs will vomit for many different reasons - most of which are harmless.
However, there are many dog illnesses which can cause severe vomiting and your vet should be the one to make a diagnosis.
As Henry has already suggested, your dog may have been poisoned. Is there anything lying around the house or yard that he could have got at, or is it possible that he's stumbled upon a decomposing carcass while out in the fields?
