Data relevant to 9092 Friesian cows from 21 herds located in Germany over a period of 18 years from 1979 to 1996 were used to estimate the genetic and phenotypic effects of days open and dry period on SOS-days milk. fat and protein yields during the first three lactations. The effects of herd. season and year of calving and parity were investigated. Least squares analysis of variance showed a highly significant influence of all factors on 305-days milk. fat and protein yields. Partial linear and quadratic regression coefficients apparently showed an average increase of 3.28. 0.128 and 0.108. kg for SOS-days milk. fat and protein yields. for each additional day open. and 1.72. 0.061 and 0.057, kg of SOS-days milk, fat and protein yields. for each additional day dry. Multiple-trait maximum Likelihood was used to estimate variances and covariance. Hentabilities for first. second. third and all lactations were 0.34. 0.25. 0.24 and 0.24 for SOS-days milk. 0.30. 0.24. 0.2? and 0.31 tor fat yield, 0.29. 0.25. . 0.22 and 0.33 for protein yield. respectively. Heritability for each of days open and dry period were low and ranged from 0.04 to 0.09. Genetic correlations between different traits in all lactations were positive and ranged from 0.32 to 0.87. Phenotypic correlations ranged from 0.19 to 0.92. A days open period of 60-90 and dry period of 60 days were suggested as optimum intervals for attaining maximum milk. fat and protein yields for Friesian cows in Germany.