This study was designed to evaluate the effects of weak-intensity extremely high frequency (EHF) microwaves in a model system-the plant organism pollen grain-lacking the placebo effect, available in large populations, to ensure accurate statistical analysis, and whose sensitivity is closely relevant to animal and human biology. This study was blinded using an in vitro pollen germination technique. SUBJECTS AND STUDY INTERVENTIONS: Pollen of kiwifruit (Actinidia deliciosa) was either directly irradiated or grown in a medium prepared with irradiated water, using a CromoStim 2000, (PromoPharma, Republic of San Marino) designed for EHF microwave resonance therapy (MRT). It produces weak intensity EHF radiations (40-78 GHz), either continuous wave (cw) or modulated, at a 10 Hz-frequency, with infrared (IR) carried to 635-950 nm, and with an impedance (IPD) of 10(-21) W/Hz cm(2) and a power supply from 0 to 20 mW. Pollen-tube emergence was expressed as a percent of grains producing a tube and tube elongation was measured at 4 hours of incubation by a turbidimetric assay (A(500)) of cultures, expressed as the net absorbance increase over time 0. At days 2 and 4 during aging, both percent of germination and tube growth significantly and consistently improved over controls in kiwifruit pollen grains irradiated for 30 minutes at day 0 at 10 Hz frequency with the CromoStim 2000. Highly significant effects, either stimulant or inhibitory, were also observed on kiwifruit pollen (stressed or not) growing in a medium prepared with water previously irradiated either cw or modulated. Irradiated water affected pollen germination immediately and even after several days following EHF treatment. Either direct or indirect EHF irradiation performed by the CromoStim 2000 is effective on pollen growth processes. In both cases, water seemed to play a primary role. According to the quantum electrodynamical coherence theory, our work could also have implications for homeopathy, suggesting a key to explain the efficacy of high dilutions and succussion procedures.