Compounds are described which modulate the tzrosine kinase activity of p56.sup.lck and signal transduction pathways in which this enzyme is involved. The invention also relates to compounds which have immunomodulatory activity, e.g., which have immunosuppressant or immunostimulatory activity, and/or which have an antineoplastic effect. The invention further relates to compositions comprising these compounds, and methods of using them. Compounds are described which modulate the tyrosine kinase activity of p56.