The NERICA (New Rice for Africa) rice varieties, developed by the Africa Rice Center during the 1990s, are providing hopes for raising the productivity of upland rice farmers in Africa because of their reported high yield potential and adaptability to the African conditions. The varieties are new and not widely disseminated in farming communities and there is lot of interest in the donor community in knowing their potential for widespread adoption across sub-Saharan Africa (SSA). However, when a technology is new and the target population is not universally exposed it, the observed sample adoption rate and classical models of adoption widely used in adoption studies does not inform reliably on its potential adoption and constraint to it in the full population. The paper uses the Average Treatment Effect (ATE) estimation framework and data from a sample of 1467 rice farmers in Guinea to document the actual and potential adoption rates of NERICA varieties and their determinants in Guinea, a country reported to have seen the largest number of adopting farmers among the SSA countries. The results of the analysis indicate that only 37% of the sample households were exposed to NERICA rice varieties in 2001 and that 20% of the sampled rice farmers adopted NERICA The potential adoption rate for the population is estimated at 61% with the adoption gap (difference between the 61% potential adoption rate and the 20% actual adoption rate) resulting from the incomplete exposure of the population to the NERICA varieties estimated at 41%. The findings suggest a relatively large unmet demand for the NERICA varieties in Guinea that justify investment in its further dissemination in Guinea.