In (Matthew 27:5) it says that Judas Iscariot threw the 30 silver coins down in the Temple and went out and hanged himself.  Not knowing what to do with this blood money, the chief priests used it to buy the potter's field; a field to be used to bury strangers.  This is the same field Judas Iscariot had hanged himself in.

In (Acts 1:18), however, it says that Judas Iscariot used the money given him to buy a field and that there he fell headlong, that his body burst open in the middle and his intestines spilled out.

At first reading it would seem that the two accounts contradict themselves, however, they don't; both accounts are correct.  Together we see more clearly what happened to Judas Iscariot that day (the day he hanged himself).

What had happened is that the chief priests used the money that Judas Iscariot had thrown into the Temple to purchase the potter's field in Judas Iscariot's name.  In so doing, in a sense, Judas Iscariot purchased it as it was purchased in his name. This was the same field in which Judas Iscariot had hanged himself.  After hanging himself, something happened which caused Judas Iscariot's body to fall headlong, burst open and his intestines to spill out.