For estimating the ovulation time in Miniature Schnauzer dogs during the estrous cycle, radioimmunoassay of plasma estradiol-$17{eta}$ and progesterone concentrations was conducted on blood samples in 21 pregnant and 13 non pregnant dogs. When Day 0 was that plasma progesterone concentrations exceeded 4.0 ng/ml, on Day 64, parturition day, progesterone declined below 1.0 ng/ml with $0.92;{pm};0.29;ng/ml$ and when Day 0 was that plasma progesterone concentrations declined below 1.0 ng/ml, on Day -64, progesterone increased above 4.0 ng/ml with $4.56;{pm};0.87;ng/ml$. Gestational length was $63.71;{pm};1.35$ (Mean${pm}$S.D.) days from plasma progesterone concentrations exceeded 4.0 ng/ml and was $66.29;{pm};1.98$ days from first male acceptance. The plasma estradiol-$17{eta}$ concentrations reached maximum value with $28.20;{pm};2.86;pg/ml$ on Day .2, and plasma progesterone concentrations reached $5.90;{pm};0.36 ng/ml, 5.18;{pm};0.32 ng/ml on Day 0, and the maximum of 61.58;{pm};10.47 ng/ml on Day 19 and 56.05;{pm};8.86;ng/ml$ on Day 16 in pregnant and non pregnant dogs, respectively. Afterward, plasma progesterone concentrations declined below 1.0 ng/ml on Day 64 with $0.92;{pm};0.29;ng/ml$ in pregnant cycles and on Day 58 with $0.95;{pm};0.63;ng/ml$ in non pregnant dogs. No difference were found pregnant and non pregnant dogs in plasma estradiol-$17{eta}$ and progesterone concentrations (p<0.01). Based on first male acceptance (Day 0), the maximum of plasma estradiol-$17{eta}$ concentrations ($29.31;{pm};3.61;pg/ml$) occurred on Day -1 and plasma progesterone concentrations exceeded 4.0 ng/ml on Day 2 in pregnant ($5.37;{pm};0.76;ng/ml$) and non pregnant ($4.25;{pm};0.80;ng/ml$) dogs. These results suggest that in Miniature Schnauzers, the ovulation occurred when plasma progesterone concentrations exceeded 4.0 ng/ml, 3 days after plasma estradiol-$17{eta}$ peak and 2 days after first male acceptance.