Genetic and phenotypic parameters were estimated in the control line of the Klerefontein Merino sheep selection experiment. The heritability estimates of 0,247 for body mass, 0,229 for clean fleece mass and 0,369 for fibre diameter are generally lower than other published estimates. Henderson’s Method 3 and REML on a sire model produced almost identical estimates. Phenotypic, environmental and genetic correlation between the three traits were all positive low. As with many other published results, genetic correlations were characterized by large standard errors of estimation. The limitations of traditional estimators is briefly discussed.