This Phase 2 study (Study 203) has been designed to determine and compare the efficacy and safety of 188-0551 Solution and Vehicle Solution applied twice daily for up to four weeks in subjects with plaque psoriasis. Subjects will be instructed to apply the test article (188-0551 Solution or Vehicle Solution) to all psoriasis plaques within the designated Treatment Area twice daily for four weeks (Study Day 29), unless the investigator verifies the subject's psoriasis has cleared at Day 15, then test article application will be for 2 weeks (Study Day 15).

Inclusion Criteria:

1. Subject is male or non-pregnant female and is at least 18 years of age.
2. Subject has provided written informed consent.
3. Subject is willing and able to apply the test article(s) as directed.
4. Subject has a clinical diagnosis of stable plaque psoriasis.
5. Subject has an Investigator's Global Assessment (IGA) score of at least three (3 = moderate) at the Baseline Visit.
6. Females must be post-menopausal, surgically sterile or use an effective method of birth control, with a negative urine pregnancy test (UPT) at the Baseline Visit.

Exclusion Criteria:

1. Subject has spontaneously improving or rapidly deteriorating plaque psoriasis.
2. Subject has guttate, pustular, erythrodermic or other non-plaque forms of psoriasis.
3. Subject has a physical condition which, in the investigator's opinion, might impair evaluation of plaque psoriasis.
4. Subject has used any phototherapy (including laser), photo-chemotherapy or other forms of photo based therapy for the treatment of their psoriasis within 30 days prior to the Baseline Visit.
5. Subject has used any systemic tofacitinib, apremilast, methotrexate, retinoids, systemic corticosteroids [including intralesional, intra-articular, and intramuscular corticosteroids], cyclosporine or analogous products within 90 days prior to the Baseline Visit.
6. Subject has used any systemic anti-inflammatory biologic therapy.
7. Subject had prolonged exposure to natural or artificial sources of ultraviolet radiation within 30 days prior to the Baseline Visit or is intending to have such exposure during the study which in the opinion of the investigator is thought to modify the subject's disease.
8. Subject has used topical body (excluding the scalp) psoriasis therapy (including coal tar, anthralin, steroids, retinoids and vitamin D analogs) within 14 days prior to the Baseline Visit.
9. Subject has used emollients/moisturizers on areas to be treated within four hours prior to clinical evaluation at the Baseline Visit.
10. Subject is currently using lithium or Plaquenil (hydroxychloroquine).
11. Subject is currently using a beta-blocking medication (e.g., propranolol) or angiotensin converting enzyme (ACE) inhibitor at a dose that has not been stabilized, in the opinion of the investigator.
12. Subject has a history of sensitivity to corticosteroids or any of the ingredients in the test articles.
13. Subject is pregnant, lactating, or is planning to become pregnant during the study.
14. Subject is currently enrolled in an investigational drug or device study.
15. Subject has used an investigational drug or investigational device treatment within 30 days prior to the Baseline Visit.
16. Subject has been previously enrolled in this study and treated with a test article.