The production value of sheep having a high or low blood potassium level were investigated. The K level in the whole blood of the five month old lambs was determined and classified into the respective phenotype: LH and HK. The study were carried out on 871 lambs and 312 ewes. In the tested population, the frequency of gene K^H in lambs was 0.427, whereas in ewes 0.540. The average level of potassium in blood in 5 month old lambs was found to be 30.5 mmol/l in the HK phenotype and 9.3 mmol/l in the LH phenotype. The results also showed that potassium-determined phenotypes had similar body weight after birth (5.1 kg), at the age of 28 (13.3) and 100 days (30.0 kg), and at 12 months (72.3 kg). The ewes had also an approximate yield of greasy wool both from the first (about 4.5 kg) and second (6.7 kg) shearing performed at the age of 10 and 22 months. A significantly lower fertility and reproduction performance was found in ewes of the HK phenotype.