THE U.S. SUPREME COURT HAS HELD THAT A POLICE CLAIM OF PROBABLE CAUSE MAY BE SUPPORTED IN TWO WAYS: (1) BY SHOWING THAT AN INFORMANT HAD A BASIS FOR ALLEGATIONS OF CRIMINAL CONDUCT OR OF PRESENCE OF CRIMINAL EVIDENCE, AND (2) BY SHOWING AN INFORMANT'S INHERENT CREDIBILITY, OR RELIABILITY ON A PARTICULAR OCCASION. THE PROBLEMS THAT HAVE ARISEN AS COURTS HAVE ATTEMPTED TO APPLY THIS TWO-PRONG TEST CONCERN ESTABLISHING WHAT CONSTITUTES SUFFICIENT EVIDENCE REGARDING AN INFORMANT'S BASIS FOR KNOWLEDGE, INHERENT CREDIBILITY, OR RELIABILITY. A RELATED PROBLEM CONCERNS HOW CORROBORATING FACTS KNOWN BY POLICE ARE TO BE CONSIDERED IN DETERMINING THE ACCEPTABILITY OF AN INFORMANT'S INFORMATION. THE ANALYSIS INCLUDES AN OVERVIEW OF MAJOR SUPREME COURT DECISIONS ON THE INFORMANT ISSUE, FOLLOWED BY A DETAILED REVIEW OF OTHER COURT DECISIONS PERTAINING TO EACH OF THE PROBLEM AREAS. OBSCURITIES AND MAJOR DIVERGENCIES ARE POINTED OUT AND EXPLORED, AND DOCTRINAL PATHS ARE SUGGESTED. THE SUPREME COURT IS URGED TO ARTICULATE CLEARER GUIDELINES ON THE INFORMANT ISSUE.