Note 5 - Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2020

Notes Tables

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block]

	March 31,
	2020		2019
Employee and non-employee stock options		1,745,811		1,032,211
Estimated common shares issuable upon conversion of notes payable and accrued interest		-		636,234
Common stock issuable under common stock purchase warrants		3,497,099		2,509,477
		5,242,910		4,177,922