The anonymous letter stated that Lance and Sue Gates were dealing in illegal drugs and gave a detailed itinerary of the couple's operation. A police detective made an independent investigation and found that the Gates were traveling along a route described in the letter. Based on these two sources of information the detective obtained a search warrant for the Gates' residence and their automobile. The trial court ordered suppression of the 350 pounds of marijuana. The Illinois Supreme Court examined the facts in view of two previous Supreme Court decisions; Aguilar v. Texas and Spinelli v. United States. In the first of these, probable cause based on an informant's tip was held to be valid only if police set forth the source of the informant's knowledge and the reasons for believing the informant. In Spinelli, the police corroboration of the details of the tip was held to be a crucial factor. Using this two-pronged approach, the Illinois Supreme Court upheld the trial court. However, the U.S. Supreme Court's reversal abandoned this approach. It reinstated the consideration of the totality of the circumstances. This approach has traditionally been used in probable cause determinations. The majority of the Court emphasized the need for a practical, nontechnical approach and regarded the two-prong test as too rigid and technical. However, analysis of the historical developments leading to the Gates decision indicates that the two-pronged test was never overly rigid or technical. Confusion and misapplication by lower courts have produced this result. Finally, the elimination of the two-pronged test can permit major abuses of privacy. One hundred sixty-three footnotes are supplied.