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1. The investigation was carried out in successive stages, with a) an initial exploratory stage to develop an understanding of the clouds of the area, upon which the design ,of a physically meaning- ful seeding experiment could be based, b) preliminary calibration seeding trials to develop a methodology for executing the seeding operation as required by the physical hypothesis, and c) an exploratory randomized seeding experiment (HIPLEX-1) on indivi- dual, small clouds to test the seeding hypothesis. It was planned that follow-on experiments would be conducted that would move up the scale to larger cloud systems as increased understanding per- mitted, leading ultimately to an area seeding experiment; however, this is not yet possible for both scientific and support reasons. 2. A detailed multi-step physical hypothesis was formulated with emphasis on expected differences between seeded and non-seeded clouds. For each step of the hypothesis, response variables capable of being measured were defined, so that the expected dif- ferences could be monitored. For the response variables asso- ciated with each step, indications were provided of how, when and where the seed/non-seed differences were to be measured. This aspect is particularly important because it provides for deter- mining not only whether the seeding produces increased rainfa11~ but also whether the physica'l mechanism is correctly understood. 3. Physical measurements of the characteristics of candidate clouds were made and analyzed -in real-time to determine their suitability as experimental units. 4. Provisions were made for a statistical evaluation and a complemen- tary physical evaluation of the experiment. The statistica"\ eva- luation of the physically based experiment focused on establishing proof changes due to seeding and on verifying the hypothesized physical sequence of events leading to the changes (Mielke et a1., 1984). The physical evaluation focused on case studies to establish the cause-and-effect relationships, or lack thereof, of any seeding-produced modifications to the cloud and its physical mechanisms (Cooper and Lawson, 1984). Because of the experimental approach used in HIPLEX-1, it was possible to determine where, how and why seeded clouds behaved differently from natural clouds and, more important, behaved differently than hypothesized. It was possible to provide a better understanding of basic cloud processes and their response to seeding in spite of the limited data set that was available. 7. Future The SCPP, CRADP and CREST programs are based on the experimental straltegy i ntro- duced by HIPLEX-l. Indeed, we have probably seen the last of the so.,called Ib1ack-box" experiments whi ch try to re1 ate cloud seedi ng to preci pitati on on the ground while ignoring the complex chain of intermediate processes. Our ina- bi 1 ity to understand the physical reasons under1yi ng the F ACE-1 and FACE-2 11