The midcareeer learning of 120 professionals in 12 contrasting business, engineering, and health care organizations was examined to identify factors facilitating workplace learning. Individuals were interviewed regarding their current work and ways they acquired the necessary know-how and knowledge for their jobs and improved or extended their performance. After 6-12 months, 88 (73%) of the same individuals were reinterviewed about factors affecting their further learning. Most of the learning reported was nonformal and unplanned, and it arose naturally from the demands of individuals' work. Learning was enhanced under circumstances in which they perceived a challenge that had to be met. Learning was also promoted by individuals (or their work teams) actively creating their own challenges. Learning from other people was the preferred mode of learning. Learning in response to challenge was affected by how individuals were supported in the microculture of their immediate work environment and especially by their immediate manager. Managers played two roles: giving direct support and facilitating a climate for learning in which people naturally help each other to learn, seek advice, and find resources to assist them. Mutual interaction of four elements--confidence, challenge, support, and workplace--benefited individuals and entire working groups alike. (Contains 16 references) (MN)