Schwangerschaftsprotein 1 (SP1) values in serum and urine were compared. The first appearance of the protein in urine happens 9–17 days after the first SP1(-positive serum, i.e., about 9 days after the first missed period. Urinary SP1 values up to 6 weeks after LMP do not correlate with gestational age as do serum values, but towards the end of the first trimester this correlation becomes almost as good as the one obtained with serum. The urinary SP1 concentration of SP1 fluctuates around 2.3% of the serum concentration throughout pregnancy.