D was tried before a jury for conspiring to distribute phenycyclidine hydrochloride (PCP) and of possessing with intent to distribute PCP and dl-methamphetamine hydrochloride. P presented its case primarily through the testimony of two undercover agents, Robert Starratt and Douglas Driver. They testified that D had acted as a middleman or intermediary in arranging three separate drug transactions between the agents and certain individuals who had drugs for sale. D did not deny that he had participated in the drug transactions but argued that, during each of these transactions, he had proceeded upon the good faith belief that he was working for the agents, assisting them in locating drug dealers. P testified that he had learned that Starratt was an undercover agent several days before he had met the agent or engaged in any of the activities alleged in the indictment. D conceded that he never entered into any formal agreement to cooperate with the agents, but claimed there was an implied understanding that he would lead the agents to drug sources. D related a conversation he had had with his mother shortly after he met Starratt and well in advance of his arrest. D stated to his mother that person who had frequently telephoned her home asking to speak to D was a narcotics agent with whom he was then working. To corroborate his story, D called his mother as a witness. Outside the presence of the jury, she testified that D received several phone calls and I would tell him that Bob called and I questioned D on who he was because I thought at first it was a painting job and D had said told me that his name was Bob Starratt, he was working with him, he was a narcotics agent, he was working with and not to worry. P did not object. But the court ruled that the mother could not testify to 'any conversations that she had with her son or that her son had with her.' D objected to the ruling was convicted and appealed.