Traditionally, diagnosis of pregnancy is based on missed menstrual periods, nausea, and observation of the visible signs and symptoms of pregnancy.  Scientific testing supplements these, but none currently available is suitable for use in rural areas.  The immunologic slide tests are easier to transport, rapid to perform, and relatively inexpensive but less capable of early diagnosis than tube tests.  The soft cannula vacuum aspiration of the uterine contents cannot usually be done by the time these tests first become positive.  Radioimmunoassays (RIAs) are capable of very early diagnosis of pregnancy.  The basis for most pregnancy tests involves the increase of chorionic gonadotropin (HCG) produced by the placenta.  It is detected in the blood or urine.  HCG production begins within 48 hours after implantation and reaches a peak at 50-90 days after the 1st day of the last menstrual period.  A lower level is maintained throughout pregnancy and then ceases 3-10 days after delivery.  Injection of the patient's blood or urine into test animals was the beginning of bioassays.  In women with delayed menstruation, repeated doses of an estrogen-progestogen preparation during a 3-5 day period and then withdrawing the therapy will cause menstruation in nonpregnant patients but not in those who are pregnant.  Because of the danger of producing fetal malformations if pregnancy is present, this test is no longer advised.  Immunological tests are based on the capability of HCG to stimulate antibody production in test animals.  In vitro tests can detect antibodies to HCG in the animals' blood.  These antibodies are capable of neutralizing HCG in blood and urine samples from pregnant women.  In addition to the tube test with red blood cells, a slide test has been devised with latex particles coated with HCG.  Inhibition of agglutination suggests pregnancy.  RIAs are based on the same principle as immunosasays.  False-positive tests are rare.  False-negative tests are more common.  For family planning programs, false-negative tests are more important because necessary measures would be delayed, particularly if ectopic pregnancy or threatened abortion were present.  These have low HCG levels.  Pregnancy tests can also be of value for identifying HCG-producing tumors, as hydtidiform mole and choriocarcinoma which produce abnormally high levels of HCG; and in monitoring the response of these tumors to chemotherapy or as follow-up after surgery to detect recurrence.  Testicular malignancy in men may be detected by pregnancy tests as some of these tumors secrete HCG.  Bioassays are accurate but time-consuming and expensive.  Hormonal tests are unreliable and possible unsafe.  Immunoassays are accurate, convenient, and inexpensive.  The most convenient pregnancy test is the Pregnosticon Dri-Dot test which is a slide method.