Developments in instrumentation at the Cloud Simulation and Aerosol Laboratory at Colorado State University since the Second International Workshop on Condensation and Ice Nuclei are outlined. Emphasis is given to improvements in the isothermal cloud chamber and the current status of a second-generation, controlled slow-expansion cloud chamber in which ascent of an air parcel may be simulated. Work with the aerosol dilution system (wind tunnel) is also described.Tests conducted during the three years 1971 through 1973 to determine the ice nucleus production of many currently used cloud-seeding devices are summarized. Effectiveness curves for nine ground-based steady-state generators burning various solutions of AgI-NH4I and AgI-NaI in acetone are presented. Test results for three airborne generators are also given and contrasted with the results for the ground generators. Finally, effectiveness values are presented for a number of pyrotechnics manufactured by Olin, Colspan, Sierra Research, and the Naval Weapons Center.The need for caution in the use of such effectiveness curves in the design of weather modification experiments is stressed. It is believed that optimal “dosages” of artificial nuclei for natural clouds can be determined using cloud chamber measurements. But probable differences in cloud characteristics and aerosol residence times both in cloud and in transit to cloud must be taken into account. Such considerations together with a more accurate simulation of operational conditions of ventilation for different cloud-seeding devices constitute a major thrust of current research effort at the Simulation Laboratory.